Fix MAX6675_SEPARATE_SPI boot loop (#14698)

Marlin/src/module/temperature.cpp

 #include "../core/language.h"
 #include "../HAL/shared/Delay.h"
 
-#define MAX6675_SEPARATE_SPI EITHER(HEATER_0_USES_MAX6675, HEATER_1_USES_MAX6675) && PIN_EXISTS(MAX6675_SCK, MAX6675_DO)
+#define MAX6675_SEPARATE_SPI (EITHER(HEATER_0_USES_MAX6675, HEATER_1_USES_MAX6675) && PIN_EXISTS(MAX6675_SCK, MAX6675_DO))
 
 #if MAX6675_SEPARATE_SPI
   #include "../libs/private_spi.h"