Fix JyersUI for LPC176x

Marlin/src/HAL/LPC1768/HAL.h

@@ -107,7 +107,7 @@ extern DefaultSerial1 USBSerial;
     #error "LCD_SERIAL_PORT must be from 0 to 3. You can also use -1 if the board supports Native USB."
   #endif
   #if HAS_DGUS_LCD
-    #define SERIAL_GET_TX_BUFFER_FREE() MSerial0.available()
+    #define SERIAL_GET_TX_BUFFER_FREE() LCD_SERIAL.available()
   #endif
 #endif
 

Marlin/src/lcd/e3v2/jyersui/dwin.cpp

@@ -331,7 +331,7 @@ CrealityDWINClass CrealityDWIN;
               (uint16_t)round(0b111111 *  mesh_z_values[x][y] / (!viewer_asymmetric_range ? range : v_max)) << 5) | // green if mesh point value is positive
                 min(0b11111, (((uint8_t)abs(mesh_z_values[x][y]) / 10) * 4))),                                     // + blue stepping for every mm
           start_x_px, start_y_px, end_x_px, end_y_px);
-        while (LCD_SERIAL.availableForWrite() < 32) { // wait for serial to be available without blocking and resetting the MCU
+        while (SERIAL_GET_TX_BUFFER_FREE()) { // wait for serial to be available without blocking and resetting the MCU
           gcode.process_subcommands_now_P("G4 P10");
           planner.synchronize();
         }

Marlin/src/lcd/e3v2/jyersui/dwin_lcd.cpp

@@ -92,7 +92,7 @@ bool DWIN_Handshake(void) {
   #endif
   LCD_SERIAL.begin(LCD_BAUDRATE);
   const millis_t serial_connect_timeout = millis() + 1000UL;
-  while (!LCD_SERIAL && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
+  while (!LCD_SERIAL.connected() && PENDING(millis(), serial_connect_timeout)) { /*nada*/ }
 
   size_t i = 0;
   DWIN_Byte(i, 0x00);