Cleanup ImageInterface.SetImageVariation

This change modifies the interface method of
ImageInterface.SetImageVariation so that the image variation is set
directly at the caller image variation module, instead of passing the
pointer to set the image variation.

Test: m nothing
Change-Id: I8eadb5149365530243e19a8cd37eb49d335fbeef
diff --git a/genrule/genrule.go b/genrule/genrule.go
index 26dad01..06a7e18 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -650,7 +650,7 @@
 func (x noopImageInterface) DebugRamdiskVariantNeeded(android.BaseModuleContext) bool    { return false }
 func (x noopImageInterface) RecoveryVariantNeeded(android.BaseModuleContext) bool        { return false }
 func (x noopImageInterface) ExtraImageVariations(ctx android.BaseModuleContext) []string { return nil }
-func (x noopImageInterface) SetImageVariation(ctx android.BaseModuleContext, variation string, module android.Module) {
+func (x noopImageInterface) SetImageVariation(ctx android.BaseModuleContext, variation string) {
 }
 
 func NewGenSrcs() *Module {