virtio-pci: fix bus master bug setting on load

The comment suggests we're checking for the driver in the ready
state and bus master disabled, but the code is checking that it's
not in the ready state.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Found-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
