Change the first argument of SPI::wrteBytes to be const (#3242)

fixes: https://github.com/espressif/arduino-esp32/issues/3241

libraries/SPI/src/SPI.cpp

@@ -204,7 +204,7 @@ void SPIClass::transferBits(uint32_t data, uint32_t * out, uint8_t bits)
  * @param data uint8_t *
  * @param size uint32_t
  */
-void SPIClass::writeBytes(uint8_t * data, uint32_t size)
+void SPIClass::writeBytes(const uint8_t * data, uint32_t size)
 {
     if(_inTransaction){
         return spiWriteNL(_spi, data, size);

libraries/SPI/src/SPI.h

@@ -76,7 +76,7 @@ public:
     void write(uint8_t data);
     void write16(uint16_t data);
     void write32(uint32_t data);
-    void writeBytes(uint8_t * data, uint32_t size);
+    void writeBytes(const uint8_t * data, uint32_t size);
     void writePixels(const void * data, uint32_t size);//ili9341 compatible
     void writePattern(uint8_t * data, uint8_t size, uint32_t repeat);