NFC: pn544: use flags argument of devm_gpiod_get to set direction

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.

Use this to simplify the driver. Furthermore this is one caller less
that stops us making the flags argument to gpiod_get*() mandatory.

While touching this also do some minor coding style fixes.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>