mtd: sh_flctl: register sh_flctl using platform_driver_probe()

As with orion_nand in commit f33dabbe79fdf7a8568c65faa1db7794c87ac4d3
("register orion_nand using platform_driver_probe()"), avoid .init.text
problems by using platform_device_probe(). This isn't going to be
hotplugged anyway.

Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>