erasure-code/shec: use free() to release alloc()'ed memory chunk

ASan warns
```
==445793==ERROR: AddressSanitizer: alloc-dealloc-mismatch (malloc vs operator delete) on 0x602000039b10
    #0 0x5604a544112d in operator delete(void*) (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest_erasure_code_shec_all+0x1e012d) (BuildId: 8cfc74d22471b6905f9b23304aed2af945265a13)
    #1 0x7fc14752f588 in ErasureCodeShecTableCache::~ErasureCodeShecTableCache() /home/jenkins-build/build/workspace/ceph-pull-requests/src/erasure-code/shec/ErasureCodeShecTableCache.cc:61:19
    ceph#2 0x5604a544ccbe in ParameterTest_parameter_all_Test::TestBody() /home/jenkins-build/build/workspace/ceph-pull-requests/src/test/erasure-code/TestErasureCodeShec_all.cc:263:1
...
0x602000039b10 is located 0 bytes inside of 4-byte region [0x602000039b10,0x602000039b14)
allocated by thread T0 here:
    #0 0x5604a5405afe in malloc (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest_erasure_code_shec_all+0x1a4afe) (BuildId: 8cfc74d22471b6905f9b23304aed2af945265a13)
    #1 0x7fc1474c9617 in reed_sol_vandermonde_coding_matrix /home/jenkins-build/build/workspace/ceph-pull-requests/src/erasure-code/jerasure/jerasure/src/reed_sol.c:86:10
    ceph#2 0x7fc147528634 in ErasureCodeShec::shec_reedsolomon_coding_matrix(int) /home/jenkins-build/build/workspace/ceph-pull-requests/src/erasure-code/shec/ErasureCodeShec.cc:514:12
    ceph#3 0x7fc147526cd8 in ErasureCodeShecReedSolomonVandermonde::prepare() /home/jenkins-build/build/workspace/ceph-pull-requests/src/erasure-code/shec/ErasureCodeShec.cc:390:14
    ceph#4 0x7fc1475187aa in ErasureCodeShec::init(std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >&, std::ostream*) /home/jenkins-build/build/workspace/ceph-pull-requests/src/erasure-code/shec/ErasureCodeShec.cc:57:3
```

where we use `delete` to free the encoder matrix allocated using
`malloc()`. as jerasure is a library implemented in C language,
unless we want to reimplment it in C++, we should use `free()` to
free the memory chunk allocated by
`reed_sol_vandermonde_coding_matrix()`. also, please note,
jerasure does not provide a function to free the memory allocated
by this function, we have to explore its implementation, and use
`malloc()` directly. this should silence the ASan warning.

Signed-off-by: Kefu Chai <[email protected]>

src/erasure-code/shec/ErasureCodeShecTableCache.cc

@@ -58,7 +58,7 @@ ErasureCodeShecTableCache::~ErasureCodeShecTableCache()
             for (table_it = tables_it__->second.begin(); table_it != tables_it__->second.end(); ++table_it) {
               if (table_it->second) {
                 if (*(table_it->second)) {
-                  delete *(table_it->second);
+                  free(*(table_it->second));
                 }
                 delete table_it->second;
               }