drivers/rtc/rtc-omap.c: use module_platform_driver

module_platform_driver_probe() prevents driver from requesting probe
deferral.  So using module_platform_drive() to support probe deferral.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tero Kristo <t-kristo@ti.com>
Cc: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>