NFC: nxp-nci_i2c: use flags argument of devm_gpiod_get_index

Since 39b2bbe3 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for output.

Simplify driver accordingly which even makes error checking more correct
because gpiod_direction_{in,out}put might fail. Furthermore this is one
caller less that stops us making the flags argument to gpiod_get*()
mandatory.

Acked-by: Oleg Zhurakivskyy <oleg.zhurakivskyy@intel.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>