can: sja1000: remove redundant variable ret

Return value directly from register_candev() instead of
getting value from redundant variable ret.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Jinpeng Cui <cui.jinpeng2@zte.com.cn>
Link: https://lore.kernel.org/all/20220831161835.306079-1-cui.jinpeng2@zte.com.cn


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>