KVM: PIC: fix use of uninitialised variable.

Commit aea218f3 (KVM: PIC: call ack notifiers for irqs that are
dropped form irr) used an uninitialised variable to track whether an
appropriate apic had been found.  This could result in calling the ack
notifier incorrectly.

Cc: Gleb Natapov <gleb@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Avi Kivity <avi@redhat.com>