The function pointer declarations in dd.h for the BufferData() and
BufferSubData() use the ARB-suffixed datatypes.  This patch changes
the buffer_data_fallback() and buffer_sub_data_fallback() functions
to use those datatypes too.

This fixes a build warning when building 32-bit libraries.  Evidently,
GLsizeiptrARB and GLsizeiptr are defined differently in that situation.

All all implementations of these driver hooks use the ARB-suffixed
types.

Reviewed-by: Mathias Fröhlich <Mathias.Froehlich@web.de>