Make sure to not override TARGET_SYSTEM_PROP.

Overriding TARGET_SYSTEM_PROP in wahoo/device.mk file removes system properties set for Android Go devices.

Bug: 120873371
Test: Manual tests
Change-Id: Ib001e5df504e1ba5e146cd242019225aa203f385
diff --git a/device.mk b/device.mk
index 6500a80..2e791a6 100755
--- a/device.mk
+++ b/device.mk
@@ -59,7 +59,7 @@
 SRC_DISPLAY_HAL_DIR := hardware/qcom/display/msm8998
 SRC_CAMERA_HAL_DIR := hardware/qcom/camera/msm8998
 
-TARGET_SYSTEM_PROP := $(LOCAL_PATH)/system.prop
+TARGET_SYSTEM_PROP := $(TARGET_SYSTEM_PROP) $(LOCAL_PATH)/system.prop
 
 # Get kernel-headers
 $(call inherit-product, hardware/qcom/msm8998/msm8998.mk)