hwrng: omap - Move probe function to .devinit.text

A pointer to omap_rng_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: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Jan Engelhardt <jengelh@gmx.de>
Cc: Michael Buesch <mb@bu3sch.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>