dm: remove unnecessary (void*) conversion in event_callback()

Pointer variables of void * type do not require type cast.
Signed-off-by: XU pengfei <xupengfei@nfschina.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm.c

@@ -2144,7 +2144,7 @@ static void event_callback(void *context)
 {
 	unsigned long flags;
 	LIST_HEAD(uevents);
-	struct mapped_device *md = (struct mapped_device *) context;
+	struct mapped_device *md = context;
 
 	spin_lock_irqsave(&md->uevent_lock, flags);
 	list_splice_init(&md->uevent_list, &uevents);