fs: encode_fh: return FILEID_INVALID if invalid fid_type

This patch is a follow up on below patch:

[PATCH] exportfs: add FILEID_INVALID to indicate invalid fid_type
commit: 216b6cbdcb

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Vivek Trivedi <t.vivek@samsung.com>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Acked-by: Sage Weil <sage@inktank.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/isofs/export.c

@@ -125,10 +125,10 @@ isofs_export_encode_fh(struct inode *inode,
 	 */
 	if (parent && (len < 5)) {
 		*max_len = 5;
-		return 255;
+		return FILEID_INVALID;
 	} else if (len < 3) {
 		*max_len = 3;
-		return 255;
+		return FILEID_INVALID;
 	}
 
 	len = 3;