watchdog: lantiq_wdt: Remove the un-necessary check of resource after platform_get_resource()

devm_ioremap_resource() checks for valid resource.
Remove the un-necessary check after platform_get_resource().

Signed-off-by: George Cherian <george.cherian@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>