mtd: nand: xway: fix build because of module functions

Remove the usage of modules functions to make this driver compile
again. Otherwise an include of linux/modules.h would be needed.

Fixes: 02436675 ("mtd: nand: xway: convert to normal platform driver")
Cc: <stable@vger.kernel.org>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>