KVM: PPC: Update int_pending also on dequeue

When having a decrementor interrupt pending, the dequeuing happens manually
through an mtdec instruction. This instruction simply calls dequeue on that
interrupt, so the int_pending hint doesn't get updated.

This patch enables updating the int_pending hint also on dequeue, thus
correctly enabling guests to stay in guest contexts more often.

Signed-off-by: Alexander Graf <agraf@suse.de>