mfd: htc-egpio: Use devm_ioremap_nocache() instead of ioremap_nocache()

Replace probe-time ioremap_nocache() call with devm_ioremap_nocache()
to avoid iounmap() missing and get rid of the corresponding iounmap()
call on remove.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Lee Jones <lee.jones@linaro.org>