hal: Fix for adev_open causing hang

- Mutex acquired in the begining of
  the synchronised block but is not
  unlocked when platform_init fails.

- Fix by adding the mutex unlock code.

Change-Id: I02b7f7cac0185dd40ec9f03e443e4de98b18c105
CRs-fixed: 590216
diff --git a/hal/audio_hw.c b/hal/audio_hw.c
index fc78610..bf08eb8 100644
--- a/hal/audio_hw.c
+++ b/hal/audio_hw.c
@@ -2593,6 +2593,7 @@
         free(adev);
         ALOGE("%s: Failed to init platform data, aborting.", __func__);
         *device = NULL;
+        pthread_mutex_unlock(&adev_init_lock);
         return -EINVAL;
     }