Rename product_services to system_ext

Bug: 134359158
Test: build and check if system_ext.img is created
Change-Id: Ice3229baf97a94c24a6eea22e7d4571941d7f843
diff --git a/android/paths.go b/android/paths.go
index 20b8b82..0ea4447 100644
--- a/android/paths.go
+++ b/android/paths.go
@@ -1145,8 +1145,8 @@
 		partition = ctx.DeviceConfig().OdmPath()
 	} else if ctx.ProductSpecific() {
 		partition = ctx.DeviceConfig().ProductPath()
-	} else if ctx.ProductServicesSpecific() {
-		partition = ctx.DeviceConfig().ProductServicesPath()
+	} else if ctx.SystemExtSpecific() {
+		partition = ctx.DeviceConfig().SystemExtPath()
 	} else {
 		partition = "system"
 	}