f2fs: introduce f2fs_i_size_write with mark_inode_dirty_sync

This patch introduces f2fs_i_size_write() to call mark_inode_dirty_sync() with
i_size_write().

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 9fa8d3e..dc4beae 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -686,7 +686,7 @@
 	drop_nlink(inode);
 	if (S_ISDIR(inode->i_mode)) {
 		drop_nlink(inode);
-		i_size_write(inode, 0);
+		f2fs_i_size_write(inode, 0);
 	}
 	up_write(&F2FS_I(inode)->i_sem);
 	update_inode_page(inode);