gpio: Remove VLA from xra1403 driver

The new challenge is to remove VLAs from the kernel
(see https://lkml.org/lkml/2018/3/7/621

)

This patch replaces a VLA with an appropriate call to kmalloc_array.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>