f2fs: persist system.advise into on-disk inode

This patch fixes to dirty inode for persisting i_advise of f2fs inode info into
on-disk inode if user sets system.advise through setxattr. Otherwise the new
value will be lost.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/xattr.c

@@ -153,6 +153,7 @@ static int f2fs_xattr_advise_set(struct dentry *dentry, const char *name,
 		return -EINVAL;
 
 	F2FS_I(inode)->i_advise |= *(char *)value;
+	mark_inode_dirty(inode);
 	return 0;
 }