cifs: fix potential mismatch of UNC paths

Ensure that full_path is an UNC path that contains '\\' as delimiter,
which is required by cifs_build_devname().

The build_path_from_dentry_optional_prefix() function may return a
path with '/' as delimiter when using SMB1 UNIX extensions, for
example.
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>

fs/cifs/cifs_dfs_ref.c

@@ -324,6 +324,8 @@ static struct vfsmount *cifs_dfs_do_automount(struct dentry *mntpt)
 	if (full_path == NULL)
 		goto cdda_exit;
 
+	convert_delimiter(full_path, '\\');
+
 	cifs_dbg(FYI, "%s: full_path: %s\n", __func__, full_path);
 
 	if (!cifs_sb_master_tlink(cifs_sb)) {