agm: plugins: Fix incompatible function pointer type error

Change-Id: Ibb1e200ca552167b09c3e6d47855f5611193f596
diff --git a/plugins/tinyalsa/src/agm_pcm_plugin.c b/plugins/tinyalsa/src/agm_pcm_plugin.c
index 8eb6587..2444e72 100644
--- a/plugins/tinyalsa/src/agm_pcm_plugin.c
+++ b/plugins/tinyalsa/src/agm_pcm_plugin.c
@@ -862,22 +862,16 @@
     return munmap(addr, length);
 }
 
-static int agm_pcm_ioctl(struct pcm_plugin *plugin, int cmd, ...)
+static int agm_pcm_ioctl(struct pcm_plugin *plugin, int cmd, __unused void *arg)
 {
     struct agm_pcm_priv *priv = plugin->priv;
     uint64_t handle;
     int ret = 0;
-    va_list ap;
-    void *arg;
 
     ret = agm_get_session_handle(priv, &handle);
     if (ret)
         return ret;
 
-    va_start(ap, cmd);
-    arg = va_arg(ap, void *);
-    va_end(ap);
-
     switch (cmd) {
     case SNDRV_PCM_IOCTL_RESET:
         ret = agm_pcm_plugin_reset(plugin);