Fix an incorrect LOG_ALWAYS_FATAL_IF introduced in sweep

* flip the condition to get same functionality as before the
  sweep

Bug: None
Test: None
Change-Id: Iae781f495f29357431d84e79207849f9c3659d94
diff --git a/libs/vr/libeds/distortion_renderer.cpp b/libs/vr/libeds/distortion_renderer.cpp
index 59029d8..13090ca 100644
--- a/libs/vr/libeds/distortion_renderer.cpp
+++ b/libs/vr/libeds/distortion_renderer.cpp
@@ -308,7 +308,7 @@
   if (blend_with_previous_layer) {
     // Check for unsupported shader combinations:
     LOG_ALWAYS_FATAL_IF(num_layers != 1);
-    LOG_ALWAYS_FATAL_IF(!use_alpha_vignette);
+    LOG_ALWAYS_FATAL_IF(use_alpha_vignette);
     if (kUseFramebufferReadback)
       frag_builder += "#define BLEND_WITH_PREVIOUS_LAYER\n";
   }