can: flexcan: fix bus-off error state handling.

Making sure that the bus-off state gets passed to can_change_state().

Signed-off-by: Andri Yngvason <andri.yngvason@marel.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>