KVM: Properly lock PIT creation

Otherwise, two threads can create a PIT in parallel and cause a memory leak.

Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/i8254.c

@@ -548,9 +548,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm)
 	if (!pit)
 		return NULL;
 
-	mutex_lock(&kvm->lock);
 	pit->irq_source_id = kvm_request_irq_source_id(kvm);
-	mutex_unlock(&kvm->lock);
 	if (pit->irq_source_id < 0) {
 		kfree(pit);
 		return NULL;