virtio-pci: thinko fix

virtio-pci: thinko fix

Since patch ed757e140c0ada220f213036e4497315d24ca8bct, virtio will
sometimes clear all status registers on bus master disable, which loses
information such as VIRTIO_CONFIG_S_FAILED bit.  This is a result of
a patch being misapplied: code uses !  instead of ~ for bit
operations as in Yan's original patch.  This obviously does not make
sense.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>