ossaudio: fix memory leak

Variable "conf" going out of scope leaks the storage
it points to in line 856.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Message-Id: <1435021270-7768-1-git-send-email-arei.gonglei@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
