misc: eeprom_93xx46: Simplify the usage of gpiod API

Commit 3ca9b1ac ("misc: eeprom_93xx46: Add support for a GPIO
'select' line.") introduced the optional usage of 'select-gpios'
by using the gpiod API in a convoluted way.

Rewrite the gpiod handling to make the code simpler.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>