drivers/rtc/rtc-omap.c: update to devm_* API

Update the code to use devm_* API so that driver core will manage
resources.

Signed-off-by: Vishwanathrao Badarkhe, Manish <manishv.b@ti.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>