docs: i2c: old-module-parameters: use monospace instead of ""

Use a monospace (literal) formatting for better readability of sysfs
attributes and the "dummy" client name. This looks much more readable in
ReST-generated output.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>