drivers: can: mcux: flexcan: can_set_mode supports can_mode_3_samples

In case CAN-FD mode is not enabled the mcux flexcan driver supports
CAN_MODE_3_SAMPLES.
This has been removed inadvertently while adding can-fd support.

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>
(cherry picked from commit 8009ccce)