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: 216b6cbdcbd86b1db0754d58886b466ae31f5a63

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>
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index 614f34a..81ee29e 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -22,10 +22,10 @@
 
 	if (parent && (len < BTRFS_FID_SIZE_CONNECTABLE)) {
 		*max_len = BTRFS_FID_SIZE_CONNECTABLE;
-		return 255;
+		return FILEID_INVALID;
 	} else if (len < BTRFS_FID_SIZE_NON_CONNECTABLE) {
 		*max_len = BTRFS_FID_SIZE_NON_CONNECTABLE;
-		return 255;
+		return FILEID_INVALID;
 	}
 
 	len  = BTRFS_FID_SIZE_NON_CONNECTABLE;