watchdog: omap_wdt: eliminate unused variable and a compiler warning

We forgot to delete this in the commit 4f4753d9 (watchdog: omap_wdt:
convert to devm_ functions), and as a result the following compilation
warning was introduced:

drivers/watchdog/omap_wdt.c: In function 'omap_wdt_remove':
drivers/watchdog/omap_wdt.c:299:19: warning: unused variable 'res' [-Wunused-variable]
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/omap_wdt.c

@@ -296,7 +296,6 @@ static int omap_wdt_remove(struct platform_device *pdev)
 {
 	struct watchdog_device *wdog = platform_get_drvdata(pdev);
 	struct omap_wdt_dev *wdev = watchdog_get_drvdata(wdog);
-	struct resource *res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 
 	pm_runtime_disable(wdev->dev);
 	watchdog_unregister_device(wdog);