smsc9420: fix another postfixed timeout

Roel Kluin recently fixed several instances where variables reach -1,
but 0 is tested afterwards.  This patch fixes another, so the timeout
will be correctly detected and a warning printed.
Signed-off-by: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/smsc9420.c

@@ -341,7 +341,7 @@ static int smsc9420_eeprom_send_cmd(struct smsc9420_pdata *pd, u32 op)
 	do {
 		msleep(1);
 		e2cmd = smsc9420_reg_read(pd, E2P_CMD);
-	} while ((e2cmd & E2P_CMD_EPC_BUSY_) && (timeout--));
+	} while ((e2cmd & E2P_CMD_EPC_BUSY_) && (--timeout));
 
 	if (!timeout) {
 		smsc_info(HW, "TIMED OUT");