gpiolib: remove duplicate inclusions

Remove second `#include <linux/err.h>`. Remove `#include <asm/errno.h>`
too as it's included by `err.h`.

Signed-off-by: Wang Jinchao <wangjinchao@xfusion.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>