aout: fix aout_CheckChannelExtraction return value

This function returns true if channel extraction is needed.

If layouts are the same, channel extraction should be needed only if the number
of channels is different.

src/audio_output/common.c

@@ -511,7 +511,7 @@ bool aout_CheckChannelExtraction( int *pi_selection,
         if( pi_selection[i] != i )
             return true;
     }
-    return i_out == i_channels;
+    return i_out != i_channels;
 }
 
 /* Return the order in which filters should be inserted */