can: can327: fix a broken link to Documentation

Since commit 482a4360

 ("docs: networking: convert netdevices.txt to
ReST"), Documentation/networking/netdevices.txt has been replaced by
Documentation/networking/netdevices.rst.

Update the comment accordingly to avoid a 'make htmldocs' warning.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/all/6a54aff884ea4f84b661527d75aabd6632140715.1659249135.git.christophe.jaillet@wanadoo.fr
Fixes: 43da2f07

 ("can: can327: CAN/ldisc driver for ELM327 based OBD-II adapters")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>