KVM: x86: Fix pv tlb flush dependencies

PV TLB FLUSH can only be turned on when steal time is enabled.
The condition got reversed during conflict resolution.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Fixes: 4f2f61fc ("KVM: X86: Avoid traversing all the cpus for pv tlb flush when steal time is disabled")
[Rebased on top of kvm/master and reworded the commit message. - Radim]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>