[jme] Fix 64-bit compile of JMicron ethernet driver

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/jme.c

 		txbi = txring->bufinf[i];
 
 		if (txbi && !(txdesc[i].descwb.flags & TXWBFLAG_OWN)) {
-			DBG2("TX clean address: %08lx(%08lx+%x)\n",
+			DBG2("TX clean address: %08lx(%08lx+%zx)\n",
 					(unsigned long)txbi->data,
 					virt_to_bus(txbi->data),
 					iob_len(txbi));