i965: Silence unused parameter warnings in get_buffer_rect

i965: Silence unused parameter warnings in get_buffer_rect

brw_meta_fast_clear.c: In function 'get_buffer_rect':
brw_meta_fast_clear.c:318:37: warning: unused parameter 'brw' [-Wunused-parameter]
 get_buffer_rect(struct brw_context *brw, struct gl_framebuffer *fb,
                                     ^
brw_meta_fast_clear.c:319:44: warning: unused parameter 'irb' [-Wunused-parameter]
                 struct intel_renderbuffer *irb, struct rect *rect)
                                            ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>