block: use the right type for stub rq_integrity_vec()

For !CONFIG_BLK_DEV_INTEGRITY, rq_integrity_vec() wasn't updated
properly. Fix it up.

Fixes: cf546dd2 ("block: change rq_integrity_vec to respect the iterator")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blk-integrity.h

@@ -145,7 +145,7 @@ static inline int blk_integrity_rq(struct request *rq)
 	return 0;
 }
 
-static inline struct bio_vec *rq_integrity_vec(struct request *rq)
+static inline struct bio_vec rq_integrity_vec(struct request *rq)
 {
 	/* the optimizer will remove all calls to this function */
 	return (struct bio_vec){ };