greybus: build: android: fix strip module build step

Currently, the greybus module .ko files are quite large and the
following error was observed during Android build for each greybus module:
strip: Unable to recognise the format of the input file `<module>`

Fix the strip build step by replacing the undefined KERNEL_TOOLCHAIN_PATH
variable with the GREYBUS_CC_PREFIX variable.  Also used as the
CROSS_COMPILER value for the module make.
Signed-off-by: Michael Scott <michael.scott@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Android.mk

@@ -28,5 +28,5 @@ build-greybus: $(INSTALLED_KERNEL_TARGET)
 	$(MAKE) -j$(MAKE_JOBS) CROSS_COMPILE=$(GREYBUS_CC_PREFIX) $(ARGS)
 	mkdir -p $(GREYBUS_MODULE_OUT_PATH)
 	ko=`find $(GREYBUS_SRC_PATH) -type f -name "*.ko"`;\
-	for i in $$ko; do $(KERNEL_TOOLCHAIN_PATH)strip --strip-unneeded $$i;\
+	for i in $$ko; do $(GREYBUS_CC_PREFIX)strip --strip-unneeded $$i;\
 	mv $$i $(GREYBUS_MODULE_OUT_PATH)/; done;