f2fs: flush inode metadata when checkpoint is doing

This patch registers all the inodes which have dirty metadata to sync when
checkpoint is doing.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 0635304..1965351 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -670,6 +670,7 @@
 	if (dn->nid == dn->inode->i_ino) {
 		remove_orphan_inode(sbi, dn->nid);
 		dec_valid_inode_count(sbi);
+		f2fs_inode_synced(dn->inode);
 	} else {
 		sync_inode_page(dn);
 	}