watchdog: shwdt: Remove the unnecessary check of resource after platform_get_resource()

devm_ioremap_resource check for a valid resource. Remove the unnecessary check.
Also group platform_get_resource and devm_ioremap_resource together for better
readability.

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>