iommu/amd: Return an error if vCPU affinity is set for non-vCPU IRTE

Return -EINVAL instead of success if amd_ir_set_vcpu_affinity() is
invoked without use_vapic; lying to KVM about whether or not the IRTE was
configured to post IRQs is all kinds of bad.

Fixes: d98de49 ("iommu/amd: Enable vAPIC interrupt remapping mode by default")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250404193923.1413163-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

drivers/iommu/amd/iommu.c

@@ -3879,7 +3879,7 @@ static int amd_ir_set_vcpu_affinity(struct irq_data *data, void *vcpu_info)
 	 * we should not modify the IRTE
 	 */
 	if (!dev_data || !dev_data->use_vapic)
-		return 0;
+		return -EINVAL;
 
 	ir_data->cfg = irqd_cfg(data);
 	pi_data->ir_data = ir_data;