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>
diff --git a/drivers/rtc/rtc-ds1553.c b/drivers/rtc/rtc-ds1553.c
index f98a83a1..46da571 100644
--- a/drivers/rtc/rtc-ds1553.c
+++ b/drivers/rtc/rtc-ds1553.c
@@ -407,7 +407,7 @@
 
 static __exit void ds1553_exit(void)
 {
-	return platform_driver_unregister(&ds1553_rtc_driver);
+	platform_driver_unregister(&ds1553_rtc_driver);
 }
 
 module_init(ds1553_init);