net: phy: at803x: simplify using devm_gpiod_get_optional and its 4th argument

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.
Moreover use devm_gpiod_get_optional instead of ignoring all errors
returned by devm_gpiod_get and simplify accordingly.

The result is more strict error handling which is good.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>