i2c: pnx: Use devm_*() functions

Use devm_*() functions to make cleanup paths 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>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>