Don't pass ":=" in variable name to AndroidMkEntries.SetString.

Fixes typos in https://r.android.com/1897972.

Test: m SOONG_CONFIG_art_module_source_build=false nothing
Bug: 204136549
Change-Id: I768c21bc99bfb4978fcf7f4f3631eef866e76764
diff --git a/apex/prebuilt.go b/apex/prebuilt.go
index 5b070c6..84bdcdd 100644
--- a/apex/prebuilt.go
+++ b/apex/prebuilt.go
@@ -257,8 +257,8 @@
 		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
 			func(ctx android.AndroidMkExtraEntriesContext, entries *android.AndroidMkEntries) {
 				entries.SetString("LOCAL_MODULE_PATH", p.installDir.ToMakePath().String())
-				entries.SetString("LOCAL_SOONG_INSTALLED_MODULE :=", filepath.Join(p.installDir.String(), fi.stem()))
-				entries.SetString("LOCAL_SOONG_INSTALL_PAIRS :=",
+				entries.SetString("LOCAL_SOONG_INSTALLED_MODULE", filepath.Join(p.installDir.String(), fi.stem()))
+				entries.SetString("LOCAL_SOONG_INSTALL_PAIRS",
 					fi.builtFile.String()+":"+filepath.Join(p.installDir.String(), fi.stem()))
 
 				// soong_java_prebuilt.mk sets LOCAL_MODULE_SUFFIX := .jar  Therefore