SPI performance tweak

Marlin/src/HAL/LPC1768/include/SPI.h

 class SPIClass {
   public:
     void begin();
-    void beginTransaction(SPISettings);
+    void beginTransaction(const SPISettings&);
     void endTransaction() {};
     uint8_t transfer(uint8_t data);
     uint16_t transfer16(uint16_t data);

Marlin/src/HAL/STM32F1/SPI.cpp

   _currentSetting->spi_d->regs->CR1 = cr1 | (dataMode & (SPI_CR1_CPOL|SPI_CR1_CPHA));
 }
 
-void SPIClass::beginTransaction(uint8_t pin, SPISettings settings) {
+void SPIClass::beginTransaction(uint8_t pin, const SPISettings &settings) {
   setBitOrder(settings.bitOrder);
   setDataMode(settings.dataMode);
   setDataSize(settings.dataSize);
   begin();
 }
 
-void SPIClass::beginTransactionSlave(SPISettings settings) {
+void SPIClass::beginTransactionSlave(const SPISettings &settings) {
   setBitOrder(settings.bitOrder);
   setDataMode(settings.dataMode);
   setDataSize(settings.dataSize);

Marlin/src/HAL/STM32F1/SPI.h

     bitOrder = inBitOrder;
     dataMode = inDataMode;
     dataSize = inDataSize;
+    //state    = SPI_STATE_IDLE;
   }
   uint32_t clock;
   uint32_t dataSize;
    */
   void end();
 
-  void beginTransaction(SPISettings settings) { beginTransaction(BOARD_SPI_DEFAULT_SS, settings); }
-  void beginTransaction(uint8_t pin, SPISettings settings);
+  void beginTransaction(const SPISettings &settings) { beginTransaction(BOARD_SPI_DEFAULT_SS, settings); }
+  void beginTransaction(uint8_t pin, const SPISettings &settings);
   void endTransaction();
 
-  void beginTransactionSlave(SPISettings settings);
+  void beginTransactionSlave(const SPISettings &settings);
 
   void setClockDivider(uint32_t clockDivider);
   void setBitOrder(BitOrder bitOrder);