🐛 Fix MKS Gen L 2.1 MOSFET pins (MarlinFirmware#25542)

Author: ellensp

Marlin/src/pins/ramps/pins_MKS_GEN_L_V21.h

@@ -38,7 +38,8 @@
 // Heaters / Fans
 //
 // Power outputs EFBF or EFBE
-#define MOSFET_D_PIN                           7
+#define MOSFET_B_PIN                           7
+#define FAN_PIN                                9
 
 //
 // CS Pins wired to avoid conflict with the LCD