can: dev: prevent potential information leak in can_fill_info()

The "bec" struct isn't necessarily always initialized. For example, the
mcp251xfd_get_berr_counter() function doesn't initialize anything if the
interface is down.

Fixes: 52c793f2

 ("can: netlink support for bus-error reporting and counters")
Link: https://lore.kernel.org/r/YAkaRdRJncsJO8Ve@mwanda
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>