Use soong_config_get/set instead of raw variable accesses

The raw variable accesses are breaking the rbc product config CI.

Test: ./build/bazel/ci/rbc_dashboard.py --quick factory_husky-trunk_staging-userdebug factory_ripcurrent factory_shiba
Change-Id: Ied0b29d9eeae65fb94900258627247b0a4145bc5
diff --git a/gps/brcm/device.mk b/gps/brcm/device.mk
index 3065542..45b4eb0 100644
--- a/gps/brcm/device.mk
+++ b/gps/brcm/device.mk
@@ -1,14 +1,12 @@
 BOARD_VENDOR_SEPOLICY_DIRS += device/google/gs-common/gps/brcm/sepolicy
 
 PRODUCT_SOONG_NAMESPACES += vendor/broadcom/gps/bcm47765
-
-SOONG_CONFIG_NAMESPACES += gpssdk
-SOONG_CONFIG_gpssdk += sdkv1
-SOONG_CONFIG_gpssdk_sdkv1 ?= false
-
-SOONG_CONFIG_NAMESPACES += gpssdk
-SOONG_CONFIG_gpssdk += gpsmcuversion
-SOONG_CONFIG_gpssdk_gpsmcuversion ?= gpsv2_$(TARGET_BUILD_VARIANT)
+ifeq (,$(call soong_config_get,gpssdk,sdkv1))
+    $(call soong_config_set,gpssdk,sdkv1,false)
+endif
+ifeq (,$(call soong_config_get,gpssdk,gpsmcuversion))
+    $(call soong_config_set,gpssdk,gpsmcuversion,gpsv2_$(TARGET_BUILD_VARIANT))
+endif
 
 PRODUCT_PACKAGES += \
 	bcm47765_gps_package \