KVM: Really fix HV_X64_MSR_APIC_ASSIST_PAGE

Commit 0945d4b228 tried to fix the get_msr path for the
HV_X64_MSR_APIC_ASSIST_PAGE msr, but was poorly tested.  We should be
returning 0 if the read succeeded, and passing the value back to the
caller via the pdata out argument, not returning the value directly.
Signed-off-by: Mike Waychison <mikew@google.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -1826,7 +1826,8 @@ static int get_msr_hyperv(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 	case HV_X64_MSR_TPR:
 		return kvm_hv_vapic_msr_read(vcpu, APIC_TASKPRI, pdata);
 	case HV_X64_MSR_APIC_ASSIST_PAGE:
-		return vcpu->arch.hv_vapic;
+		data = vcpu->arch.hv_vapic;
+		break;
 	default:
 		pr_unimpl(vcpu, "Hyper-V unhandled rdmsr: 0x%x\n", msr);
 		return 1;