can: flexcan: invoke flexcan_chip_freeze() to enter freeze mode

Invoke flexcan_chip_freeze() to enter freeze mode, since need poll
freeze mode acknowledge.

Fixes: e955cead ("CAN: Add Flexcan CAN controller driver")
Link: https://lore.kernel.org/r/20210218110037.16591-4-qiangqing.zhang@nxp.com


Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>