mtd: atmel nand: fix gpio missing request

without this the gpio will not be muxed as a gpio by the current custom pinmux
or later by the pinctrl

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>