Fix MacOSX build in strict mode:

[HamedSabri-adsk]

Compiler:

XCode 11.3.1

Error:

format specifies type 'unsigned long long' but the argument has type 'int' [-Werror,-Wformat]
TF_DEBUG(ALUSDMAYA_SELECTION).Msg("ProxyShapeSelection::TransformReference::decRef %" PRIu64 " %" PRIu64 " %" PRIu64 "\n", m_selected, m_refCount, m_required);
.....

Hi @murphyeoin,
I am trying to understand some of the logics in ProxyShape.h related to this issue:
So we have a bit field struct that is a size of 8bytes (16 bits * 4)

    // ref counting values
    struct
    {
      uint64_t m_required:16; 
      uint64_t m_selectedTemp:16;
      uint64_t m_selected:16;
      uint64_t m_refCount:16;
    };

but then we have these getters that return them as 4 bytes. Is there a reason for that? couldn't we return them as uint16_t.

   uint32_t selected() const { return m_selected; }
   uint32_t required() const { return m_required; }
   uint32_t refCount() const { return m_refCount; }