mmc/omap: make mmci-omap using platform_driver_probe

A pointer to mmc_omap_probe which lives in .init.text is passed to the
core via platform_driver_register and so the kernel might oops if probe
is called after the init code is discarded.

As requested by David Brownell platform_driver_probe is used instead of
moving the probe function to .devinit.text.  This saves some memory, but
might have the downside that a device being registered after the call to
mmc_omap_init but before the init sections are discarded will not be
bound anymore to the driver.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>