hw/audio/via-ac97: skip automatic zero-init of large array

hw/audio/via-ac97: skip automatic zero-init of large array

The 'out_cb' method has a 4k byte array used for copying data
between the audio backend and device. Skip the automatic zero-init
of this array to eliminate the performance overhead in the I/O hot
path.

The 'tmpbuf' array will be fully initialized when reading data from
device memory.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20250610123709.835102-14-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>