KVM: nVMX: Restore a preemption timer consistency check

A recently added preemption timer consistency check was unintentionally
dropped when the consistency checks were being reorganized to match the
SDM's ordering.

Fixes: 461b4ba4

 ("KVM: nVMX: Move the checks for VM-Execution Control Fields to a separate helper function")
Cc: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>