watchdog: bcm63xx_wdt: use devm_ioremap_nocache()

Use devm_ioremap_nocache() to make cleanup paths simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>