Followup patch for TMC stepper init

Marlin/src/module/stepper_indirection.cpp

@@ -258,7 +258,7 @@
 
   #define _TMC2208_DEFINE_HARDWARE(ST) TMC2208Stepper stepper##ST(&ST##_HARDWARE_SERIAL)
   #define _TMC2208_DEFINE_SOFTWARE(ST) SoftwareSerial ST##_HARDWARE_SERIAL = SoftwareSerial(ST##_SERIAL_RX_PIN, ST##_SERIAL_TX_PIN); \
-                                       TMC2208Stepper stepper##ST(&stepper##ST##_serial, ST##_SERIAL_RX_PIN > -1)
+                                       TMC2208Stepper stepper##ST(&ST##_HARDWARE_SERIAL, ST##_SERIAL_RX_PIN > -1)
 
   // Stepper objects of TMC2208 steppers used
   #if ENABLED(X_IS_TMC2208)