block: move req_set_nomerge to blk.h

This makes it available outside of blk-merge.c, and inlining such a trivial
helper seems pretty useful to start with.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk.h b/block/blk.h
index 4972b98d..3e08703 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -256,6 +256,13 @@ static inline int blk_do_io_stat(struct request *rq)
 		!blk_rq_is_passthrough(rq);
 }
 
+static inline void req_set_nomerge(struct request_queue *q, struct request *req)
+{
+	req->cmd_flags |= REQ_NOMERGE;
+	if (req == q->last_merge)
+		q->last_merge = NULL;
+}
+
 /*
  * Internal io_context interface
  */