KVM: x86: properly update ready_for_interrupt_injection

The recent changes to emulate string instructions without entering guest
mode exposed a bug where pending interrupts are not properly reflected
in ready_for_interrupt_injection.

The result is that userspace overwrites a previously queued interrupt,
when irqchip's are emulated in userspace.

Fix by always updating state before returning to userspace.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>