watchdog: iTCO_wdt: Report error if timeout configuration fails

The driver probes with the invalid timeout value when
'iTCO_wdt_set_timeout()' fails, as its return value is not checked. In
this case, when executing "wdctl", we may get:

Device: /dev/watchdog0
Timeout: 30 seconds
Timeleft: 613 seconds

The timeout value is the value of "heartbeat" or "WATCHDOG_TIMEOUT", and
the timeleft value is calculated from the register value we actually read
(0xffff) by masking with 0x3ff and converting ticks to seconds (* 6 / 10).

Add error handling to return the failure code if 'iTCO_wdt_set_timeout()'
fails, ensuring the driver probe fails and prevents invalid operation.

Signed-off-by: Ziyan Fu <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

drivers/watchdog/iTCO_wdt.c

···
 	/* Check that the heartbeat value is within it's range;
 	   if not reset to the default */
 	if (iTCO_wdt_set_timeout(&p->wddev, heartbeat)) {
-		iTCO_wdt_set_timeout(&p->wddev, WATCHDOG_TIMEOUT);
+		ret = iTCO_wdt_set_timeout(&p->wddev, WATCHDOG_TIMEOUT);
+		if (ret != 0) {
+			dev_err(dev, "Failed to set watchdog timeout (%d)\n", WATCHDOG_TIMEOUT);
+			return ret;
+		}
 		dev_info(dev, "timeout value out of range, using %d\n",
 			WATCHDOG_TIMEOUT);
 		heartbeat = WATCHDOG_TIMEOUT;