drivers/rtc/rtc-ab3100.c: add missing platform_set_drvdata() in ab3100_rtc_probe()

Otherwise, calling platform_get_drvdata() in ab3100_rtc_remove() returns
NULL.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
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>