ios: correct AudioUnit config for 5.1 channel

ios/IJKMediaPlayer/IJKMediaPlayer/ijkmedia/ijksdl/ios/IJKSDLAudioQueueController.m

@@ -47,6 +47,7 @@
 
         /* Get the current format */
         _spec.format = AUDIO_S16SYS;
+        _spec.channels = 2;
         AudioStreamBasicDescription streamDescription;
         IJKSDLGetAudioStreamBasicDescriptionFromSpec(&_spec, &streamDescription);
 

ios/IJKMediaPlayer/IJKMediaPlayer/ijkmedia/ijksdl/ios/IJKSDLAudioUnitController.m

@@ -72,6 +72,7 @@
 
         /* Get the current format */
         _spec.format = AUDIO_S16SYS;
+        _spec.channels = 2;
         AudioStreamBasicDescription streamDescription;
         IJKSDLGetAudioStreamBasicDescriptionFromSpec(&_spec, &streamDescription);