hw/audio/marvell_88w8618: skip automatic zero-init of large array

The 'mv88w8618_audio_callback' 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 'buf' 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: 20250610123709.835102-12-berrange@redhat.com
[Fixed hw/audio/gus in commit message --Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/audio/marvell_88w8618.c

@@ -66,7 +66,7 @@ static void mv88w8618_audio_callback(void *opaque, int free_out, int free_in)
 {
     mv88w8618_audio_state *s = opaque;
     int16_t *codec_buffer;
-    int8_t buf[4096];
+    QEMU_UNINITIALIZED int8_t buf[4096];
     int8_t *mem_buffer;
     int pos, block_size;