Stem name should be fixed the same was as masterFile

BUG: 159641682
Test: TH

Change-Id: Ic0300676c35821cedc693eeb7b970318790f6189
diff --git a/java/app.go b/java/app.go
index 245c586..e2e3a53 100755
--- a/java/app.go
+++ b/java/app.go
@@ -150,7 +150,7 @@
 				"allow-prereleased": strconv.FormatBool(proptools.Bool(as.properties.Prerelease)),
 				"screen-densities":  screenDensities,
 				"sdk-version":       ctx.Config().PlatformSdkVersion(),
-				"stem":              ctx.ModuleName(),
+				"stem":              as.BaseModuleName(),
 			},
 		})
 }