rtc: rtc-coh901331: use devm_ioremap_resource()

Use devm_ioremap_resource() in order to make the code simpler, and
remove redundant return value check of platform_get_resource() because
the value is checked by devm_ioremap_resource().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>