vhost: reset metadata cache when initializing new IOTLB

[ Upstream commit b13f9c6364373a1b9f71e9846dc4fb199296f926 ]

We need to reset metadata cache during new IOTLB initialization,
otherwise the stale pointers to previous IOTLB may be still accessed
which will lead a use after free.

Reported-by:  <syzbot+c51e6736a1bf614b3272@syzkaller.appspotmail.com>
Fixes: f8894913 ("vhost: introduce O(1) vq metadata cache")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>