cookies: switch to toybox md5sum

 * fixes "error: MD5SUM is obsolete."

Change-Id: I38e167e24e9eb5596a1e8e2f2d915f648bc1283c
diff --git a/build/tasks/cookies.mk b/build/tasks/cookies.mk
index 7388e63..6c5099a 100644
--- a/build/tasks/cookies.mk
+++ b/build/tasks/cookies.mk
@@ -1,8 +1,10 @@
 
 OMNI_TARGET_PACKAGE := $(PRODUCT_OUT)/omni-$(ROM_VERSION).zip
 
+MD5 := prebuilts/build-tools/path/$(HOST_OS)-x86/md5sum
+
 .PHONY: cookies
 cookies: $(INTERNAL_OTA_PACKAGE_TARGET)
 	$(hide) ln -f $(INTERNAL_OTA_PACKAGE_TARGET) $(OMNI_TARGET_PACKAGE)
-	$(hide) $(MD5SUM) $(OMNI_TARGET_PACKAGE) | sed "s|$(PRODUCT_OUT)/||" > $(OMNI_TARGET_PACKAGE).md5sum
+	$(hide) $(MD5) $(OMNI_TARGET_PACKAGE) | sed "s|$(PRODUCT_OUT)/||" > $(OMNI_TARGET_PACKAGE).md5sum
 	@echo -e "Package complete: $(OMNI_TARGET_PACKAGE)" >&2