net: pch_gbe: Propagate error from devm_gpio_request_one()

If GPIO controller is not available yet we need to defer
the probe of GBE until provider will become available.

While here, drop GPIOF_EXPORT because it's deprecated and
may not be available.

Fixes: f1a26fdf ("pch_gbe: Add MinnowBoard support")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Flavio Suligoi <f.suligoi@asem.it>
Signed-off-by: David S. Miller <davem@davemloft.net>