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: Wei Tang <tangwei@cmss.chinamobile.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/genhd.c b/block/genhd.c
index e5cafa5..78140b4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1421,7 +1421,7 @@
 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)
 {