Fix non-sensical values for Zonestar themistor table (#11816)

Values taken from Zonestar firmware for P802QA with a Melzi board. Timestamps from the firmware package are from April 2016.

Marlin/thermistortable_501.h

@@ -28,8 +28,8 @@ const short temptable_501[][2] PROGMEM = {
    {OV(  19), 280},
    {OV(  23), 270},
    {OV(  27), 260},
-   {OV(  32), 250},
-   {OV(  30), 240},
+   {OV(  31), 250},
+   {OV(  37), 240},
    {OV(  47), 230},
    {OV(  57), 220},
    {OV(  68), 210},