drivers/rtc/rtc-ds1216.c: use module_platform_driver_probe()

Use module_platform_driver_probe() macro which makes the code smaller and
simpler.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
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>