Fix DUE HAL serial defines (#15536)

Marlin/src/HAL/HAL_DUE/HAL.h

@@ -38,22 +38,39 @@
 
 #include <stdint.h>
 
-// Serial ports
-#if !WITHIN(SERIAL_PORT, -1, 3)
-  #error "SERIAL_PORT must be from -1 to 3"
+// Define MYSERIAL0/1 before MarlinSerial includes!
+#if SERIAL_PORT == -1
+  #define MYSERIAL0 Serial1
+#elif SERIAL_PORT == 0
+  #define MYSERIAL0 Serial
+#elif SERIAL_PORT == 1
+  #define MYSERIAL0 Serial1
+#elif SERIAL_PORT == 2
+  #define MYSERIAL0 Serial2
+#elif SERIAL_PORT == 3
+  #define MYSERIAL0 Serial3
+#else
+  #error "The required SERIAL_PORT must be from -1 to 3. Please update your configuration."
 #endif
 
-// MYSERIAL0 required before MarlinSerial includes!
-#define MYSERIAL0 customizedSerial1
-
 #ifdef SERIAL_PORT_2
-  #if !WITHIN(SERIAL_PORT_2, -1, 3)
-    #error "SERIAL_PORT_2 must be from -1 to 3"
-  #elif SERIAL_PORT_2 == SERIAL_PORT
-    #error "SERIAL_PORT_2 must be different than SERIAL_PORT"
+  #if SERIAL_PORT_2 == SERIAL_PORT
+    #error "SERIAL_PORT_2 must be different from SERIAL_PORT. Please update your configuration."
+  #endif
+  #if SERIAL_PORT_2 == -1
+    #define MYSERIAL1 Serial1
+  #elif SERIAL_PORT_2 == 0
+    #define MYSERIAL1 Serial
+  #elif SERIAL_PORT_2 == 1
+    #define MYSERIAL1 Serial1
+  #elif SERIAL_PORT_2 == 2
+    #define MYSERIAL1 Serial2
+  #elif SERIAL_PORT_2 == 3
+    #define MYSERIAL1 Serial3
+  #else
+    #error "SERIAL_PORT_2 must be from -1 to 3. Please update your configuration."
   #endif
   #define NUM_SERIAL 2
-  #define MYSERIAL1 customizedSerial2
 #else
   #define NUM_SERIAL 1
 #endif