mesa: Silence unused parameter warnings in bufferobj.c

mesa: Silence unused parameter warnings in bufferobj.c

main/bufferobj.c: In function 'count_buffer_size':
main/bufferobj.c:520:26: warning: unused parameter 'key' [-Wunused-parameter]
 count_buffer_size(GLuint key, void *data, void *userData)
                          ^
main/bufferobj.c: In function 'flush_mapped_buffer_range_fallback':
main/bufferobj.c:740:56: warning: unused parameter 'index' [-Wunused-parameter]
                                    gl_map_buffer_index index)
                                                        ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>