rtc-core: fix memory leak

The idr should be destroyed when the module is unloaded. Found with
kmemleak.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: stable <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/class.c

@@ -226,6 +226,7 @@ static void __exit rtc_exit(void)
 {
 	rtc_dev_exit();
 	class_destroy(rtc_class);
+	idr_destroy(&rtc_idr);
 }
 
 subsys_initcall(rtc_init);