ext4: fix out-of-date comments in extents.c

In this patch, ext4_ext_try_to_merge has been change to merge 
an extent both left and right.  So we need to update the comment
in here.
Signed-off-by: NHaiboLiu <HaiboLiu6@gmail.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/extents.c

@@ -1891,11 +1891,10 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
 	nearex->ee_len = newext->ee_len;
 
 merge:
-	/* try to merge extents to the right */
+	/* try to merge extents */
 	if (!(flag & EXT4_GET_BLOCKS_PRE_IO))
 		ext4_ext_try_to_merge(inode, path, nearex);
 
-	/* try to merge extents to the left */
 
 	/* time to correct all indexes above */
 	err = ext4_ext_correct_indexes(handle, inode, path);