Prepare for changing audio_pcm_ops dynamically (partially revert r5422)

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5435 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/audio/esdaudio.c b/audio/esdaudio.c
index 6339dda..f5dc1be 100644
--- a/audio/esdaudio.c
+++ b/audio/esdaudio.c
@@ -566,7 +566,7 @@
     {NULL, 0, NULL, NULL, NULL, 0}
 };
 
-static const struct audio_pcm_ops qesd_pcm_ops = {
+static struct audio_pcm_ops qesd_pcm_ops = {
     qesd_init_out,
     qesd_fini_out,
     qesd_run_out,