block: do not initialise statics to 0 or NULL

This patch fixes the checkpatch.pl error to genhd.c:

ERROR: do not initialise statics to 0 or NULL
Signed-off-by: NWei Tang <tangwei@cmss.chinamobile.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/genhd.c

@@ -1421,7 +1421,7 @@ static DEFINE_MUTEX(disk_events_mutex);
 static LIST_HEAD(disk_events);
 
 /* disable in-kernel polling by default */
-static unsigned long disk_events_dfl_poll_msecs	= 0;
+static unsigned long disk_events_dfl_poll_msecs;
 
 static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
 {