Update thermistornames.h (#16027)

Marlin/src/lcd/thermistornames.h

   #define THERMISTOR_NAME "User Parameters"
 
 // Thermcouples
+#elif THERMISTOR_ID == -5
+  #define THERMISTOR_NAME "MAX31865"
 #elif THERMISTOR_ID == -4
   #define THERMISTOR_NAME "AD8495"
 #elif THERMISTOR_ID == -3