Documentation: coding-style: Fix indentation in code-blocks

- Remove spaces in C code-blocks to align error labels consistently
- Replace tab characters with spaces in emacs-lisp code blocks

Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240202231316.7606-1-thorsten.blum@toblux.com