rtc: do not return void value

This patch fixes these sparse warnings:

drivers/rtc/rtc-ds1742.c:265:2: warning: returning void-valued expression
drivers/rtc/rtc-ds1553.c:409:2: warning: returning void-valued expression

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: David Brownell <david-b@pacbell.net>
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>