Fix variant conditional for 1284p

Marlin/softspi.h

@@ -195,7 +195,7 @@ static const pin_map_t pinMap[] = {
 || defined(__AVR_ATmega324__)\
 || defined(__AVR_ATmega16__)
 
-#ifdef defined(VARIANT_MIGHTY)
+#if defined(VARIANT_MIGHTY)
 // Mighty Layout
 static const pin_map_t pinMap[] = {
   {&DDRB, &PINB, &PORTB, 0},  // B0  0