r600g: remove set-but-unused variable

src/gallium/drivers/r600/r600_buffer.c

 				      struct pipe_transfer *transfer)
 {
 	struct r600_resource_buffer *rbuffer = r600_buffer(transfer->resource);
-	int write = 0;
 	uint8_t *data;
 
 	if (rbuffer->r.b.user_ptr)
 		return (uint8_t*)rbuffer->r.b.user_ptr + transfer->box.x;
 
-	if (transfer->usage & PIPE_TRANSFER_WRITE) {
-		write = 1;
-	}
 	data = r600_bo_map((struct radeon*)pipe->winsys, rbuffer->r.bo, transfer->usage, pipe);
 	if (!data)
 		return NULL;