`backlight.c`: include `eeprom.h` (#13024)

quantum/backlight/backlight.c

@@ -17,6 +17,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "quantum.h"
 #include "backlight.h"
+#include "eeprom.h"
 #include "eeconfig.h"
 #include "debug.h"