Btrfs: fix the comment typo for btrfs_attach_transaction_barrier

The comment is for btrfs_attach_transaction_barrier, not for
btrfs_attach_transaction. Fix the typo.

Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
Acked-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index c916ebd..bcfa32c 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -529,7 +529,7 @@
 }
 
 /*
- * btrfs_attach_transaction() - catch the running transaction
+ * btrfs_attach_transaction_barrier() - catch the running transaction
  *
  * It is similar to the above function, the differentia is this one
  * will wait for all the inactive transactions until they fully