coding-style.rst: Avoid comma statements

Commas are not how statements are terminated.
Always use semicolons and braces if necessary.

Signed-off-by: Joe Perches <joe@perches.com>
Link: https://lore.kernel.org/r/2a97b738bba335434461a5a918053a49c1fb6af4.1598331148.git.joe@perches.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>