tests: exit(1) if no valid test format supported

If RGBA8 & BGRA8 support is not found, exit(1) and not exit(0).
diff --git a/tests/vktestframework.cpp b/tests/vktestframework.cpp
index 3323cf4..ef8e4a2 100644
--- a/tests/vktestframework.cpp
+++ b/tests/vktestframework.cpp
@@ -224,7 +224,7 @@
     }
     printf("Error - device does not support VK_FORMAT_B8G8R8A8_UNORM nor "
            "VK_FORMAT_R8G8B8A8_UNORM - exiting\n");
-    exit(0);
+    exit(1);
 }
 
 void VkTestFramework::Finish() {}