bcache: fix a comments typo in bch_alloc_sectors()

Code comments in alloc.c:bch_alloc_sectors() mentions a function
name find_data_bucket(), the correct function name should be
pick_data_bucket() indeed. bch_alloc_sectors() is a quite important
function in bcache allocation code, fixing the typo may help
other people to have less confusion.
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Tang Junhui <tang.junhui@zte.com.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/alloc.c

@@ -601,7 +601,7 @@ bool bch_alloc_sectors(struct cache_set *c, struct bkey *k, unsigned sectors,
 
 	/*
 	 * If we had to allocate, we might race and not need to allocate the
-	 * second time we call find_data_bucket(). If we allocated a bucket but
+	 * second time we call pick_data_bucket(). If we allocated a bucket but
 	 * didn't use it, drop the refcount bch_bucket_alloc_set() took:
 	 */
 	if (KEY_PTRS(&alloc.key))