block: make bio_integrity_map_user() static inline

If CONFIG_BLK_DEV_INTEGRITY isn't set, then the dummy helper must be
static inline to avoid complaints about the function being unused.

Fixes: fe8f4ca ("block: modify bio_integrity_map_user to accept iov_iter as argument")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202411300229.y7h60mDg-lkp@intel.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

include/linux/bio-integrity.h

@@ -105,7 +105,7 @@ static inline void bioset_integrity_free(struct bio_set *bs)
 {
 }
 
-static int bio_integrity_map_user(struct bio *bio, struct iov_iter *iter)
+static inline int bio_integrity_map_user(struct bio *bio, struct iov_iter *iter)
 {
 	return -EINVAL;
 }