Makefile: fix upload syntax for serial port

Makefile

@@ -79,5 +79,5 @@ upload-%:
 	if [ -z '$(PORT)' ]; then \
 		$(CURL) -v --data-binary @fpga/output/$*.fw http://$(ip)/sys/fwupdate ; \
 	else \
-		$(PERL) ./esp32/flashesp.pl --port $(PORT) fpga/output/$*.fw ; \
+		$(PERL) ./esp32/flashesp.pl fpga/output/$*.fw '$(PORT)' $(FLASHOPT); \
 	fi