Correctly handle prebuilt kernel's wifi module.

When specifying a perbuilt kernel, the wifi module should also be
specifiable.
Now we allow
 make -j8 TARGET_PREBUILT_WIFI_MODULE=/my_kernel_dir/drivers/net/wireless/bcm4329/bcm4329.ko TARGET_PREBUILT_KERNEL=/my_kernel_dir/arch/arm/boot/zImage

Change-Id: Iccd3db49205d43952a4540136006220bf57dc3ba
Signed-off-by: JP Abgrall <jpa@google.com>
diff --git a/device_base.mk b/device_base.mk
index 799ee9f..705820e 100644
--- a/device_base.mk
+++ b/device_base.mk
@@ -139,8 +139,14 @@
 PRODUCT_LOCALES := hdpi
 
 
+ifeq ($(TARGET_PREBUILT_WIFI_MODULE),)
+LOCAL_WIFI_MODULE := device/samsung/crespo/bcm4329.ko
+else
+LOCAL_WIFI_MODULE := $(TARGET_PREBUILT_WIFI_MODULE)
+endif
+
 PRODUCT_COPY_FILES += \
-	device/samsung/crespo/bcm4329.ko:system/modules/bcm4329.ko
+	$(LOCAL_WIFI_MODULE):system/modules/bcm4329.ko
 
 ifeq ($(TARGET_PREBUILT_KERNEL),)
 LOCAL_KERNEL := device/samsung/crespo/kernel