Add basic output on success

Whilst it is true that "silence is golden", no output at all could be
disconcerting and it makes searching in a CI log more difficult.

Add a simple status message that says "Checked N files, style ok".

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/scripts/code_style.py b/scripts/code_style.py
index 5d05fd8..f333c64 100755
--- a/scripts/code_style.py
+++ b/scripts/code_style.py
@@ -199,6 +199,8 @@
     else:
         # Check mode
         if check_style_is_correct(src_files):
+            print("Checked {} files, style ok.".format(len(src_files)),
+                  file=STDOUT_UTF8)
             return 0
         else:
             return 1