Fix spca50x camlib compilation warnings.
Fix spca50x camlib compilation warnings.

* spca50x_get_avi(...): Cast buffer size result from pointer arithmetic to 'unsigned int' for string printing.
* spca50x_sdram_get_info(...): Change 'index' variable type to signed as it is derived from and compared to signed variables. Negative 'index' values would result in segfault so the signed comparison is safe.
* spca50x_get_FATs(...): Add some casts to 'unsigned int' in comparisons. This does not change behavior, but suppresses compiler warnings. Also change 'buf' variable type to 'char' as it is only used with string operations.

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2