tinyalsa: add pcm_get_subdevice()

The users of tinyalsa had no way of knowing on which subdevice a stream had
been created.  A new API, "unsigned int pcm_get_subdevice(struct *pcm)" returns
it.  This information is filled during the pcm_open()

Change-Id: Ie866e10e06ce6691ede09e2ca46a24441723ea8b
Signed-off-by: David Wagner <david.wagner@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

include/tinyalsa/asoundlib.h

@@ -179,6 +179,9 @@ unsigned int pcm_bytes_to_frames(struct pcm *pcm, unsigned int bytes);
 int pcm_get_htimestamp(struct pcm *pcm, unsigned int *avail,
                        struct timespec *tstamp);
 
+/* Returns the subdevice on which the pcm has been opened */
+unsigned int pcm_get_subdevice(struct pcm *pcm);
+
 /* Write data to the fifo.
  * Will start playback on the first write or on a write that
  * occurs after a fifo underrun.

pcm.c

@@ -171,6 +171,7 @@ struct pcm {
     void *mmap_buffer;
     unsigned int noirq_frames_per_msec;
     long pcm_delay;
+    unsigned int subdevice;
 };
 
 unsigned int pcm_get_buffer_size(struct pcm *pcm)
@@ -183,6 +184,11 @@ const char* pcm_get_error(struct pcm *pcm)
     return pcm->error;
 }
 
+unsigned int pcm_get_subdevice(struct pcm *pcm)
+{
+    return pcm->subdevice;
+}
+
 static int oops(struct pcm *pcm, int e, const char *fmt, ...)
 {
     va_list ap;
@@ -654,6 +660,7 @@ struct pcm *pcm_open(unsigned int card, unsigned int device,
         oops(pcm, errno, "cannot get info");
         goto fail_close;
     }
+    pcm->subdevice = info.subdevice;
 
     param_init(&params);
     param_set_mask(&params, SNDRV_PCM_HW_PARAM_FORMAT,