pcm: Get values from kernel in avail_update

Instead of sending appl_ptr and avail_min to the kernel,
get them. This is the behavior of alsa-lib.

Signed-off-by: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
diff --git a/src/pcm.c b/src/pcm.c
index 4bc86aa..3a8d4e9 100644
--- a/src/pcm.c
+++ b/src/pcm.c
@@ -1325,7 +1325,7 @@
 
 int pcm_avail_update(struct pcm *pcm)
 {
-    pcm_sync_ptr(pcm, 0);
+    pcm_sync_ptr(pcm, SNDRV_PCM_SYNC_PTR_APPL|SNDRV_PCM_SYNC_PTR_AVAIL_MIN);
     return pcm_mmap_avail(pcm);
 }