Quick hack fix for USB accessory audio support

tinyalsa fails to retrieve the correct value for the period count
from the f_audio_source driver and tries to use zero instead.
This wasn't a problem before because the usb audio HAL used hard coded values
that were compatible with the driver.

Bug: 16799652
Change-Id: I6f5b907a0699c58b071e9f419ed8e053a7d9dc77

modules/usbaudio/alsa_device_proxy.c

@@ -66,6 +66,13 @@ void proxy_prepare(alsa_device_proxy * proxy, alsa_device_profile* profile,
     proxy->alsa_config.period_size =
             profile_get_period_size(proxy->profile, proxy->alsa_config.rate);
 
+    // Hack for USB accessory audio.
+    // Here we set the correct value for period_count if tinyalsa fails to get it from the
+    // f_audio_source driver.
+    if (proxy->alsa_config.period_count == 0) {
+        proxy->alsa_config.period_count = 4;
+    }
+
     proxy->pcm = NULL;
 }