blktap: Fix wild ptr deref during device destruction.

A put_disk() before blk_cleanup_queue() would free gd before gd->queue
is read.

Signed-off-by: Daniel Stodden <daniel.stodden@xxxxxxxxxx>

diff -r 7d0b5bd0725f -r 46943b8f83b5 drivers/xen/blktap/device.c
--- a/drivers/xen/blktap/device.c	Fri Feb 05 11:12:24 2010 -0800
+++ b/drivers/xen/blktap/device.c	Wed Feb 24 16:18:30 2010 -0800
@@ -1027,8 +1027,8 @@
 #endif
 
 	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->gd->queue);
 	put_disk(dev->gd);
-	blk_cleanup_queue(dev->gd->queue);
 
 	dev->gd = NULL;