dm kcopyd: switch to use REQ_OP_WRITE_ZEROES

It seems like the code currently passes whatever it was using for writes
to WRITE SAME.  Just switch it to WRITE ZEROES, although that doesn't
need any payload.

Untested, and confused by the code, maybe someone who understands it
better than me can help..
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/md/dm-kcopyd.c

@@ -733,11 +733,11 @@ int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
 		job->pages = &zero_page_list;
 
 		/*
-		 * Use WRITE SAME to optimize zeroing if all dests support it.
+		 * Use WRITE ZEROES to optimize zeroing if all dests support it.
 		 */
-		job->rw = REQ_OP_WRITE_SAME;
+		job->rw = REQ_OP_WRITE_ZEROES;
 		for (i = 0; i < job->num_dests; i++)
-			if (!bdev_write_same(job->dests[i].bdev)) {
+			if (!bdev_write_zeroes_sectors(job->dests[i].bdev)) {
 				job->rw = WRITE;
 				break;
 			}