[MTD] [NAND] move gen_nand's probe function to .devinit.text

A pointer to plat_nand_probe is passed to the core via
platform_driver_register and so the function must not disappear when the
.init sections are discarded.  Otherwise (if also having HOTPLUG=y)
unbinding and binding a device to the driver via sysfs will result in an
oops as does a device being registered late.

An alternative to this patch is using platform_driver_probe instead of
platform_driver_register plus removing the pointer to the probe function
from the struct platform_driver.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Hamish Moffatt <hamish@cloud.net.au>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>