Change return value of I2S:: availableForWrite to match new Print API

Author: sandeepmistry

libraries/I2S/src/I2S.cpp

@@ -280,7 +280,7 @@ size_t I2SClass::write(const uint8_t *buffer, size_t size)
   return write((const void*)buffer, size);
 }
 
-size_t I2SClass::availableForWrite()
+int I2SClass::availableForWrite()
 {
   if (_state != I2S_STATE_TRANSMITTER) {
     enableTransmitter();

libraries/I2S/src/I2S.h

@@ -51,7 +51,7 @@ class I2SClass : public Stream
   virtual size_t write(uint8_t);
   virtual size_t write(const uint8_t *buffer, size_t size);
 
-  virtual size_t availableForWrite();
+  virtual int availableForWrite();
 
   int read(void* buffer, size_t size);