HID: mcp2221: set gpio pin mode

in case we have GPIOLIB enabled the gpio pins are used
from the current driver as gpio pins. But may the gpio
functions of this pins are not enabled in the flash
of the chip and so gpio access fails.

In case CONFIG_IIO is not enabled we can prevent this
issue of the driver simply by enabling the gpio mode
for all pins.

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Jiri Kosina <jkosina@suse.com>