KVM: SEV: fix double locking due to incorrect backport

Fix an incorrect line in the 5.4.y and 4.19.y backports of commit
19a23da ("Fix unsynchronized access to sev members through
svm_register_enc_region"), first applied to 5.4.98 and 4.19.176.

Fixes: 1e80fdc ("KVM: SVM: Pin guest memory when SEV is active")
Reported-by: Dov Murik <dovmurik@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org # 5.4.x
Cc: stable@vger.kernel.org # 4.19.x
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/kvm/svm.c

@@ -7104,7 +7104,6 @@ static int svm_register_enc_region(struct kvm *kvm,
 	region->uaddr = range->addr;
 	region->size = range->size;
 
-	mutex_lock(&kvm->lock);
 	list_add_tail(&region->list, &sev->regions_list);
 	mutex_unlock(&kvm->lock);