Fix the section mismatch warning

WARNING: vmlinux.o(.text+0x2b2788): Section mismatch in reference from the function mxc_gpio_probe() to the function .init.text:mxc_gpio_init_gc()
The function mxc_gpio_probe() references
the function __init mxc_gpio_init_gc().
This is often because mxc_gpio_probe lacks a __init
annotation or the annotation of mxc_gpio_init_gc is wrong.
Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>