clear DMA progress flag on end and make it volatile

Author: sandeepmistry

libraries/I2S/src/I2S.cpp

@@ -116,14 +116,15 @@ void I2SClass::end()
     DMA.freeChannel(_dmaChannel);
   }
 
+  _dmaTransferInProgress = false;
+
   i2sd.disableSerializer(_deviceIndex);
   i2sd.disableClockUnit(_deviceIndex);
 
   pinMode(_sdPin, INPUT);
   pinMode(_fsPin, INPUT);
   pinMode(_sckPin, INPUT);
 
-
   disableClock();
 
   _beginCount--;

libraries/I2S/src/I2S.h

@@ -73,7 +73,7 @@ class I2SClass : public Stream
 
   int _dmaChannel;
 
-  bool _dmaTransferInProgress;
+  volatile bool _dmaTransferInProgress;
   I2SDoubleBuffer _doubleBuffer;
 
   void (*_onTransmit)(void);