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) <[e-mail]>
Signed-off-by: Steve French <[e-mail]>
Acked-by: Ronnie Sahlberg <[e-mail]>

fs/cifs/cifs_dfs_ref.c

···
 	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)) {