trivial: rtc-stk17ta8: fix sparse warning

Fix this sparse warning:

  drivers/rtc/rtc-stk17ta8.c:403:2: warning: returning void-valued expression

Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/drivers/rtc/rtc-stk17ta8.c b/drivers/rtc/rtc-stk17ta8.c
index f4cd46e..549990f 100644
--- a/drivers/rtc/rtc-stk17ta8.c
+++ b/drivers/rtc/rtc-stk17ta8.c
@@ -400,7 +400,7 @@
 
 static __exit void stk17ta8_exit(void)
 {
-	return platform_driver_unregister(&stk17ta8_rtc_driver);
+	platform_driver_unregister(&stk17ta8_rtc_driver);
 }
 
 module_init(stk17ta8_init);