can: flexcan: flexcan_chip_stop(): add error handling and propagate error value

This patch implements error handling and propagates the error value of
flexcan_chip_stop(). This function will be called from flexcan_suspend()
in an upcoming patch in some SoCs which support LPSR mode.

Add a new function flexcan_chip_stop_disable_on_error() that tries to
disable the chip even in case of errors.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
[mkl: introduce flexcan_chip_stop_disable_on_error() and use it in flexcan_close()]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20200922144429.2613631-11-mkl@pengutronix.de