KVM: Move kvm_guest_exit() after local_irq_enable()

We need to make sure that the timer interrupt happens before we clear
PF_VCPU, so the accounting code actually sees guest mode.

http://lkml.org/lkml/2007/10/15/114

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>