omap_hsmmc: add missing probe handler hook

The missing probe handler hook will never probe the driver. Add it back.
Fixes broken MMC on OMAP.

We use platform_driver_probe() API since omap_hsmmc is not a hot-pluggable
device.

Signed-off-by: Roger Quadros <ext-roger.quadros@nokia.com>
Tested-by: Felipe Contreras <felipe.contreras@gmail.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Felipe Contreras <felipe.contreras@gmail.com>
Cc: Denis Karpov <ext-denis.2.karpov@nokia.com>
Cc: Madhusudhan Chikkature <madhu.cr@ti.com>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>