watchdog: omap: use watchdog_init_timeout instead of open coding it

Instead of (partly) open coding watchdog_init_timeout to determine the
inital timeout use the core function that exists for exactly this
purpose.

As a side effect the "timeout-sec" device-tree property is recognized now
(though currently unused in the omap device trees).

Signed-off-by: Uwe Kleine-König <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

Documentation/devicetree/bindings/watchdog/omap-wdt.txt

···
 - compatible : "ti,omap3-wdt" for OMAP3 or "ti,omap4-wdt" for OMAP4
 - ti,hwmods : Name of the hwmod associated to the WDT
 
+Optional properties:
+- timeout-sec : default watchdog timeout in seconds
+
 Examples:
 
 wdt2: wdt@4a314000 {

drivers/watchdog/omap_wdt.c

···
 	omap_wdt->min_timeout = TIMER_MARGIN_MIN;
 	omap_wdt->max_timeout = TIMER_MARGIN_MAX;
 
-	if (timer_margin >= TIMER_MARGIN_MIN &&
-	    timer_margin <= TIMER_MARGIN_MAX)
-		omap_wdt->timeout = timer_margin;
-	else
+	if (watchdog_init_timeout(omap_wdt, timer_margin, &pdev->dev) < 0)
 		omap_wdt->timeout = TIMER_MARGIN_DEFAULT;
 
 	watchdog_set_drvdata(omap_wdt, wdev);