[I2C] Reorder i2c_t field to avoid padding

Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/stm32/twi.h

@@ -100,13 +100,13 @@ struct i2c_s {
 #if !defined(STM32F0xx) && !defined(STM32L0xx)
   IRQn_Type irqER;
 #endif //!defined(STM32F0xx) && !defined(STM32L0xx)
-  volatile uint8_t slaveMode;
-  uint8_t isMaster;
   volatile int slaveRxNbData; // Number of accumulated bytes received in Slave mode
   void (*i2c_onSlaveReceive)(uint8_t *, int);
   void (*i2c_onSlaveTransmit)(void);
   volatile uint8_t i2cTxRxBuffer[I2C_TXRX_BUFFER_SIZE];
   volatile uint8_t i2cTxRxBufferSize;
+  volatile uint8_t slaveMode;
+  uint8_t isMaster;
 };
 
 ///@brief I2C state