can: m_can: Read register PSR only on error

Only read register PSR if there is an error indicated in irqstatus.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Link: https://lore.kernel.org/all/20221206115728.1056014-4-msp@baylibre.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>