virtio-blk: fix out-of-bounds access to bitmap in notify_guest_bh

virtio-blk: fix out-of-bounds access to bitmap in notify_guest_bh

When the number of a virtio-blk device's virtqueues is larger than
BITS_PER_LONG, the out-of-bounds access to bitmap[ ] will occur.

Fixes: e21737ab15 ("virtio-blk: multiqueue batch notify")
Cc: qemu-stable@nongnu.org
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Li Hangjing <lihangjing@baidu.com>
Reviewed-by: Xie Yongji <xieyongji@baidu.com>
Reviewed-by: Chai Wen <chaiwen@baidu.com>
Message-id: 20191216023050.48620-1-lihangjing@baidu.com
Message-Id: <20191216023050.48620-1-lihangjing@baidu.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 725fe5d10dbd4259b1853b7d253cef83a3c0d22a)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>