Properly check the tmp dir mode

This was using a boolean && instead of a bitwise mask. Reported
by covertity.

common/flatpak-dir.c

@@ -639,7 +639,7 @@ flatpak_ensure_system_user_cache_dir_location (GError **error)
       /* Must be owned by us */
       st_buf.st_uid == getuid () &&
       /* and not writeable by others */
-      (st_buf.st_mode && 0022) != 0)
+      (st_buf.st_mode & 0022) != 0)
     return g_file_new_for_path (path);
 
   path = g_strdup ("/var/tmp/flatpak-cache-XXXXXX");