Fix ArchFeatures decoding with default ArchVariant

We were using the original ArchVariant passed in, not the blank string
that we reset it to if it's considered the default variant.

Change-Id: Ice644cc1d4897af99fe79b55d441f406a7a270de
diff --git a/common/arch.go b/common/arch.go
index 23ec550..8ad5087 100644
--- a/common/arch.go
+++ b/common/arch.go
@@ -1020,7 +1020,7 @@
 	}
 
 	if featureMap, ok := archFeatureMap[archType]; ok {
-		a.ArchFeatures = featureMap[stringPtr(archVariant)]
+		a.ArchFeatures = featureMap[a.ArchVariant]
 	}
 
 	return a, nil