make: add beeps face to build

PR #386 did not add the C file to the makefile,
causing the build to fail at the link stage
due to the missing object file and the symbols
that were supposed to be provided by it.

Adding the file to the build fixes the issue.

Reported-by: CarpeNoctem <cryptomax@pm.me>
Fixed-by: CarpeNoctem <cryptomax@pm.me>
Reviewed-by: Matheus Afonso Martins Moreira <matheus@matheusmoreira.com>
GitHub-Issue: #472
Fixes: #472

Author: matheusmoreira

movement/make/Makefile

@@ -140,6 +140,7 @@ SRCS += \
   ../watch_faces/complication/simon_face.c \
   ../watch_faces/complication/simple_calculator_face.c \
   ../watch_faces/sensor/alarm_thermometer_face.c \
+  ../watch_faces/demo/beeps_face.c \
 # New watch faces go above this line.
 
 # Leave this line at the bottom of the file; it has all the targets for making your project.