can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once

can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once

If an invalid CAN frame is received, from a driver or from a tun
interface, a Kernel warning is generated.

This patch replaces the WARN_ONCE by a simple pr_warn_once, so that a
kernel, bootet with panic_on_warn, does not panic. A printk seems to be
more appropriate here.

Reported-by: [email protected]
Suggested-by: Dmitry Vyukov <[email protected]>
Acked-by: Oliver Hartkopp <[email protected]>
Cc: linux-stable <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>