block: Make blk_rq_set_mixed_merge() static

Since commit 8e756373 ("block: Move bio merge related functions into
blk-merge.c"), blk_rq_set_mixed_merge() has only been referenced in
blk-merge.c, so make it static.
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240325083501.2816408-1-john.g.garry@oracle.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-merge.c

@@ -726,7 +726,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
  *     which can be mixed are set in each bio and mark @rq as mixed
  *     merged.
  */
-void blk_rq_set_mixed_merge(struct request *rq)
+static void blk_rq_set_mixed_merge(struct request *rq)
 {
 	blk_opf_t ff = rq->cmd_flags & REQ_FAILFAST_MASK;
 	struct bio *bio;

block/blk.h

@@ -339,7 +339,6 @@ int ll_back_merge_fn(struct request *req, struct bio *bio,
 bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,
 				struct request *next);
 unsigned int blk_recalc_rq_segments(struct request *rq);
-void blk_rq_set_mixed_merge(struct request *rq);
 bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio);