Fix i2c_master.d listed more than once warning

keyboards/ergodox_ez/keymaps/default/keymap.c

@@ -1,6 +1,4 @@
 #include QMK_KEYBOARD_H
-#include "debug.h"
-#include "action_layer.h"
 #include "version.h"
 
 #define BASE 0 // default layer

keyboards/ergodox_ez/rules.mk

@@ -15,8 +15,7 @@
 #----------------------------------------------------------------------------
 
 # # project specific files
-SRC = matrix.c \
-  i2c_master.c
+SRC += matrix.c
 
 # MCU name
 MCU = atmega32u4
@@ -85,4 +84,9 @@ API_SYSEX_ENABLE = no
 RGBLIGHT_ENABLE = yes
 RGB_MATRIX_ENABLE = no # enable later
 
+ifeq ($(strip $(RGB_MATRIX_ENABLE)), no)
+  SRC += i2c_master.c
+endif
+
+
 LAYOUTS = ergodox