drivers/rtc/rtc-s3c.c: add placeholder for driver private data

Driver data field is a pointer, hence assigning that to an integer results
in compilation warnings.

Fixes following compilation warnings:

  drivers/rtc/rtc-s3c.c: In function `s3c_rtc_get_driver_data':
  drivers/rtc/rtc-s3c.c:452:3: warning: return makes integer from pointer without a cast [enabled by default]
  drivers/rtc/rtc-s3c.c: At top level:
  drivers/rtc/rtc-s3c.c:674:3: warning: initialization makes pointer from integer without a cast [enabled by default]
  drivers/rtc/rtc-s3c.c:674:3: warning: (near initialization for `s3c_rtc_dt_match[1].data') [enabled by default]
  drivers/rtc/rtc-s3c.c:677:3: warning: initialization makes pointer from integer without a cast [enabled by default]
  drivers/rtc/rtc-s3c.c:677:3: warning: (near initialization for `s3c_rtc_dt_match[2].data') [enabled by default]
  drivers/rtc/rtc-s3c.c:680:3: warning: initialization makes pointer from integer without a cast [enabled by default]
  drivers/rtc/rtc-s3c.c:680:3: warning: (near initialization for `s3c_rtc_dt_match[3].data') [enabled by default]

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>