RN42 Bluetooth typo fix (#14421)

common_features.mk

@@ -764,7 +764,7 @@ ifeq ($(strip $(BLUETOOTH_ENABLE)), yes)
     endif
 
     ifeq ($(strip $(BLUETOOTH_DRIVER)), RN42)
-        OPT_DEFS += DMODULE_RN42
+        OPT_DEFS += -DMODULE_RN42
         SRC += $(TMK_DIR)/protocol/serial_uart.c
     endif
 endif