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/android/image.go b/android/image.go
index bc6b8cd..9cad056 100644
--- a/android/image.go
+++ b/android/image.go
@@ -44,9 +44,8 @@
 	ExtraImageVariations(ctx BaseModuleContext) []string
 
 	// SetImageVariation is called for each newly created image variant. The receiver is the original
-	// module, "variation" is the name of the newly created variant and "module" is the newly created
-	// variant itself.
-	SetImageVariation(ctx BaseModuleContext, variation string, module Module)
+	// module, "variation" is the name of the newly created variant. "variation" is set on the receiver.
+	SetImageVariation(ctx BaseModuleContext, variation string)
 }
 
 const (
@@ -106,7 +105,7 @@
 		mod := ctx.CreateVariations(variations...)
 		for i, v := range variations {
 			mod[i].base().setImageVariation(v)
-			m.SetImageVariation(ctx, v, mod[i])
+			mod[i].(ImageInterface).SetImageVariation(ctx, v)
 		}
 	}
 }