Fix Wire.write() signature

Fixes arduino/ArduinoCore-nRF528x-mbedos#48

Author: facchinm

libraries/Wire/Wire.cpp

@@ -93,7 +93,7 @@ size_t arduino::MbedI2C::write(uint8_t data) {
 	return 1;
 }
 
-size_t arduino::MbedI2C::write(uint8_t* data, int len) {
+size_t arduino::MbedI2C::write(const uint8_t* data, int len) {
 	if (usedTxBuffer + len > 256) len = 256 - usedTxBuffer;
 	memcpy(txBuffer + usedTxBuffer, data, len);
 	usedTxBuffer += len;

libraries/Wire/Wire.h

@@ -45,7 +45,7 @@ class MbedI2C : public HardwareI2C
     virtual void onRequest(void(*)(void));
 
     virtual size_t write(uint8_t data);
-    virtual size_t write(uint8_t* data, int len);
+    virtual size_t write(const uint8_t* data, int len);
     virtual int read();
     virtual int peek();
     virtual void flush();