rtc: rtc-jz4740: use devm_ioremap_resource()

Use devm_ioremap_resource() in order to make the code simpler, and move
'struct resource *mem' from 'struct jz4740_rtc' to jz4740_rtc_probe()
because the 'mem' variable is used only in jz4740_rtc_probe().  Also the
redundant return value check of platform_get_resource() is removed,
because the value is checked by devm_ioremap_resource().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>