pcm: fix default capture start threshold

Default start threshold was set to the same value (half of the buffer size)
for playback and capture in pcm_open(). The normal default value for capture
should be 1 frame.

Change-Id: I05afd51ada3d915a6dde7c97846e1693f7c575f4
diff --git a/pcm.c b/pcm.c
index 4e9133a..284a7ac 100644
--- a/pcm.c
+++ b/pcm.c
@@ -547,10 +547,13 @@
     sparams.tstamp_mode = SNDRV_PCM_TSTAMP_ENABLE;
     sparams.period_step = 1;
 
-    if (!config->start_threshold)
-        pcm->config.start_threshold = sparams.start_threshold =
-            config->period_count * config->period_size / 2;
-    else
+    if (!config->start_threshold) {
+        if (pcm->flags & PCM_IN)
+            pcm->config.start_threshold = sparams.start_threshold = 1;
+        else
+            pcm->config.start_threshold = sparams.start_threshold =
+                config->period_count * config->period_size / 2;
+    } else
         sparams.start_threshold = config->start_threshold;
 
     /* pick a high stop threshold - todo: does this need further tuning */