fix possible build break

If you try to build a recovery image without having built the main
system, creating the recovery resourc file can fail due to the
directory not existing.

Change-Id: I2daff847c0b58dfa519d0f742636f01dba28c689

core/Makefile

@@ -666,6 +666,7 @@ $(INSTALLED_RECOVERYIMAGE_TARGET): $(MKBOOTFS) $(MKBOOTIMG) $(MINIGZIP) \
 	@echo ----- Made recovery image: $@ --------
 
 $(RECOVERY_RESOURCE_ZIP): $(INSTALLED_RECOVERYIMAGE_TARGET)
+	$(hide) mkdir -p $(dir $@)
 	$(hide) find $(TARGET_RECOVERY_ROOT_OUT)/res -type f | sort | zip -0qrj $@ -@
 
 else