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
19a23da53932bc ("Fix unsynchronized access to sev members through
svm_register_enc_region"), first applied to 5.4.98 and 4.19.176.

Fixes: 1e80fdc0 ("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>