watchdog: Convert to devm_ioremap_resource()

Use the newly introduced devm_ioremap_resource() instead of
devm_request_and_ioremap() which provides more consistent error handling.

devm_ioremap_resource() provides its own error messages; so all explicit
error messages can be removed from the failure code paths.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Gabor Juhos <juhosg@openwrt.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>