f2fs: introduce f2fs_commit_super

This patch introduces f2fs_commit_super to write updated superblock.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index c98454d..7ff3ac7 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1535,6 +1535,7 @@
 /*
  * super.c
  */
+int f2fs_commit_super(struct f2fs_sb_info *);
 int f2fs_sync_fs(struct super_block *, int);
 extern __printf(3, 4)
 void f2fs_msg(struct super_block *, const char *, const char *, ...);