add some cuda conversion to avoid useless conversion

[nicolas-beaufort]

This pull-request add some cuda conversion to avoid useless conversion like NV12ToBGR8.

[auroraborghi]

@nicolas-beaufort @dusty-nv
Nicolas Beaufort's code worked perfectly to solve the issue of having 0s as camera image data with the following changes to gstCamera.cpp and gstCamera.h:

• camera/gstCamera.cpp
  • CaptureRGBA (line 280): (void** output) instead of float
  • ConvertRGBA (line 302): (void** output) instead of float
• camera/gstCamera.h
  • CaptureRGBA (line 78): (void** output) instead of float
  • ConvertRGBA (line 82): (void** output) instead of float

If the appropriate changes above are made, #5 with dusty-nv/jetbot_ros#7 will solve dusty-nv/jetbot_ros#2 .