mx3/eukrea_mbimxsd-baseboard: fix gpio request

without this patch, we get :
------------[ cut here ]------------
WARNING: at drivers/gpio/gpiolib.c:99 gpio_ensure_requested+0x4c/0x104()
autorequest GPIO-4
.../...
[<c01bcfb0>] (platform_lcd_set_power+0x34/0x40) from [<c033954c>] (platform_lcd_probe+0xb8/0xd8)

Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>