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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/smsc9420.c

···
 	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");