block: Make wbt_wait() definition consistent with declaration

Fixes: e34cbd3 ("blk-wbt: add general throttling mechanism")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-wbt.c

@@ -595,7 +595,7 @@ static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
  * in an irq held spinlock, if it holds one when calling this function.
  * If we do sleep, we'll release and re-grab it.
  */
-unsigned int wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
+enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
 {
 	unsigned int ret = 0;