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

kerneldevice/mm-kernel-device-generic-rules.c: In function ‘udev_rule_clear’:
  kerneldevice/mm-kernel-device-generic-rules.c:40:5: error: switch missing default case [-Werror=switch-default]
     40 |     switch (rule->result.type) {
        |     ^~~~~~

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

@@ -48,6 +48,7 @@ udev_rule_clear (MMUdevRule *rule)
         break;
     case MM_UDEV_RULE_RESULT_TYPE_GOTO_INDEX:
     case MM_UDEV_RULE_RESULT_TYPE_UNKNOWN:
+    default:
         break;
     }