can: dev: can_get_state_str(): Remove dead code

The default switch case ends with a return; meaning this return is
never reached.

Coverity-ID: 1497123
Signed-off-by: Ariel Otilibili <ariel.otilibili-anieli@eurecom.fr>
Link: https://patch.msgid.link/20241221111454.1074285-4-ariel.otilibili-anieli@eurecom.fr


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