KVM: VMX: Fix comment to specify PID.ON instead of PIR.ON

The Outstanding Notification (ON) bit is part of the Posted Interrupt
Descriptor (PID) as opposed to the Posted Interrupts Register (PIR).
The latter is a bitmap for pending vectors.
Reviewed-by: NJoao Martins <joao.m.martins@oracle.com>
Signed-off-by: NLiran Alon <liran.alon@oracle.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -6137,7 +6137,7 @@ static int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
 	if (pi_test_on(&vmx->pi_desc)) {
 		pi_clear_on(&vmx->pi_desc);
 		/*
-		 * IOMMU can write to PIR.ON, so the barrier matters even on UP.
+		 * IOMMU can write to PID.ON, so the barrier matters even on UP.
 		 * But on x86 this is just a compiler barrier anyway.
 		 */
 		smp_mb__after_atomic();