kvm: svm: fix unsigned compare less than zero comparison

vm_data->avic_vm_id is a u32, so the check for a error
return (less than zero) such as -EAGAIN from
avic_get_next_vm_id currently has no effect whatsoever.
Fix this by using a temporary int for the comparison
and assign vm_data->avic_vm_id to this. I used an explicit
u32 cast in the assignment to show why vm_data->avic_vm_id
cannot be used in the assign/compare steps.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -1412,17 +1412,18 @@ static void avic_vm_destroy(struct kvm *kvm)
 static int avic_vm_init(struct kvm *kvm)
 {
 	unsigned long flags;
-	int err = -ENOMEM;
+	int vm_id, err = -ENOMEM;
 	struct kvm_arch *vm_data = &kvm->arch;
 	struct page *p_page;
 	struct page *l_page;
 
 	if (!avic)
 		return 0;
 
-	vm_data->avic_vm_id = avic_get_next_vm_id();
-	if (vm_data->avic_vm_id < 0)
-		return vm_data->avic_vm_id;
+	vm_id = avic_get_next_vm_id();
+	if (vm_id < 0)
+		return vm_id;
+	vm_data->avic_vm_id = (u32)vm_id;
 
 	/* Allocating physical APIC ID table (4KB) */
 	p_page = alloc_page(GFP_KERNEL);