hal : Fix for FM playback unmute

Adding fix for FM playback unmute which was not working.

Change-Id: I724323bc421692e2cae16d8d4821ed86345b784f
diff --git a/hal/audio_extn/FM.cpp b/hal/audio_extn/FM.cpp
index a2df576..a55d4c7 100644
--- a/hal/audio_extn/FM.cpp
+++ b/hal/audio_extn/FM.cpp
@@ -285,7 +285,10 @@
     if (ret >= 0) {
         ALOGD("%s: Param: mute", __func__);
         fm.muted = (value[0] == '1');
-        fm_set_volume(0);
+        if(fm.muted)
+           fm_set_volume(0);
+        else
+           fm_set_volume(fm.volume);
     }
 
     ret = str_parms_get_str(parms, AUDIO_PARAMETER_KEY_FM_RESTORE_VOLUME, value, sizeof(value));