kernel-device-generic: fix warnings with -Wswitch-default

kerneldevice/mm-kernel-device-generic.c: In function ‘check_rule’:
  kerneldevice/mm-kernel-device-generic.c:802:9: error: switch missing default case [-Werror=switch-default]
    802 |         switch (rule->result.type) {
        |         ^~~~~~

src/kerneldevice/mm-kernel-device-generic.c

@@ -844,6 +844,7 @@ check_rule (MMKernelDeviceGeneric *self,
 
         case MM_UDEV_RULE_RESULT_TYPE_GOTO_TAG:
         case MM_UDEV_RULE_RESULT_TYPE_UNKNOWN:
+        default:
             g_assert_not_reached ();
         }
     }