cinterion: fix warnings with -Wswitch-default

cinterion/mm-shared-cinterion.c: In function ‘disable_location_gathering_context_gps_step’:
  cinterion/mm-shared-cinterion.c:412:5: error: switch missing default case [-Werror=switch-default]
    412 |     switch (ctx->gps_step) {
        |     ^~~~~~
  cinterion/mm-shared-cinterion.c: In function ‘enable_location_gathering_context_gps_step’:
  cinterion/mm-shared-cinterion.c:665:5: error: switch missing default case [-Werror=switch-default]
    665 |     switch (ctx->gps_step) {
        |     ^~~~~~

plugins/cinterion/mm-shared-cinterion.c

@@ -480,6 +480,9 @@ disable_location_gathering_context_gps_step (GTask *task)
         }
         g_object_unref (task);
         return;
+
+    default:
+        g_assert_not_reached ();
     }
 }
 
@@ -735,6 +738,9 @@ enable_location_gathering_context_gps_step (GTask *task)
         g_task_return_boolean (task, TRUE);
         g_object_unref (task);
         return;
+
+    default:
+        g_assert_not_reached ();
     }
 }