x86: VMX: Fix the VMX-preemption timer expiration test

When the VMX-preemption timer fires between the test for
"vmx_get_test_stage() == 0" and the subsequent rdtsc instruction, the
final VM-entry to finish the guest will inadvertently update
vmx_preemption_timer_expiry_finish.

Move the code to finish the guest until after the calculations
involving vmx_preemption_timer_expiry_finish are done, so that it
doesn't matter if vmx_preemption_timer_expiry_finish is clobbered.

Signed-off-by: Jim Mattson <jmattson@google.com>
Fixes: b49a1a6d ("x86: VMX: Add a VMX-preemption timer expiration test")
Link: https://lore.kernel.org/r/20220629025634.666085-1-jmattson@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>