block: Fix spelling in the header above blkg_lookup()

See also commit 8f4236d9 ("block: remove QUEUE_FLAG_BYPASS and ->bypass") # v5.0.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blk-cgroup.h

@@ -375,7 +375,7 @@ static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
  * @q: request_queue of interest
  *
  * Lookup blkg for the @blkcg - @q pair.  This function should be called
- * under RCU read loc.
+ * under RCU read lock.
  */
 static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
 					   struct request_queue *q)