KVM: s390: selftests: Fix memop extension capability check

Fix the inverted logic of the memop extension capability check.

Fixes: 97da92c0 ("KVM: s390: selftests: Use TAP interface in the memop test")
Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Message-Id: <20220614162635.3445019-1-scgl@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>