coding-style: Add guidance to prefer dev_dbg

During review, it was suggested that drivers only emit messages when
something is wrong or it is a debug message. Document this as a formal
recommendation.

https://lore.kernel.org/linux-usb/2024012525-alienate-frown-916b@gregkh/



Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240125165311.1.I8d9c88e747e233917e527c7dad1feb8a18f070e2@changeid