Make M155 / M156 a bit more flexible

Marlin/Marlin_main.cpp

    */
   inline void gcode_M155() {
     // Set the target address
-    if (code_seen('A'))
-      i2c.address(code_value_byte());
+    if (code_seen('A')) i2c.address(code_value_byte());
 
     // Add a new byte to the buffer
-    else if (code_seen('B'))
-      i2c.addbyte(code_value_int());
+    if (code_seen('B')) i2c.addbyte(code_value_byte());
 
     // Flush the buffer to the bus
-    else if (code_seen('S')) i2c.send();
+    if (code_seen('S')) i2c.send();
 
     // Reset and rewind the buffer
     else if (code_seen('R')) i2c.reset();
    * Usage: M156 A<slave device address base 10> B<number of bytes>
    */
   inline void gcode_M156() {
-    uint8_t addr = code_seen('A') ? code_value_byte() : 0;
-    int bytes    = code_seen('B') ? code_value_int() : 1;
+    if (code_seen('A')) i2c.address(code_value_byte());
 
-    if (addr && bytes > 0 && bytes <= 32) {
-      i2c.address(addr);
+    uint8_t bytes = code_seen('B') ? code_value_byte() : 1;
+
+    if (i2c.addr > 0 && bytes > 0 && bytes <= 32) {
       i2c.reqbytes(bytes);
     }
     else {

Marlin/twibus.h

     const int timeout = 5;
 
     /**
-     * @brief Target device address
-     * @description The target device address. Persists until changed.
-     *              
-     */
-    uint8_t addr = 0;
-
-    /**
      * @brief Number of bytes on buffer
      * @description Number of bytes in the buffer waiting to be flushed to the bus.
      */
      * @brief Internal buffer
      * @details A fixed buffer. TWI commands can be no longer than this.
      */
-    char buffer[30];
+    char buffer[32];
 
 
   public:
     /**
+     * @brief Target device address
+     * @description The target device address. Persists until changed.
+     */
+    uint8_t addr = 0;
+
+    /**
      * @brief Class constructor
      * @details Initialize the TWI bus and clear the buffer
      */