can: m_can: m_can_get_berr_counter(): don't wake up controller if interface is down

can: m_can: m_can_get_berr_counter(): don't wake up controller if interface is down

If the interface is down, the CAN controller might be powered down, the
clock disabled, and/or it's external reset asserted.

Don't wake up the controller to read the CAN bus error counters, if the
interface is down.

Reviewed-by: Markus Schneider-Pargmann <msp@baylibre.com>
Link: https://patch.msgid.link/20251008-m_can-cleanups-v1-7-1784a18eaa84@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>