KVM: selftests: Add a missing apostrophe in comment to show ownership

Add an apostrophe in a comment about it being the caller's, not callers,
responsibility to free an object.

Reported-by: Andrew Jones <drjones@redhat.com>
Fixes: 768e9a61 ("KVM: selftests: Purge vm+vcpu_id == vcpu silliness")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220613161942.1586791-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>