can: flexcan: Disable error interrupt when bus error reporting is disabled

In case we don't have FLEXCAN_HAS_BROKEN_ERR_STATE and the user set
CAN_CTRLMODE_BERR_REPORTING once it can not be unset again until reboot.
So in case neither hardware nor user wants the error interrupt disable
the bit.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>