can: mcp251x: only reset hardware as required

This prevents unwanted glitches on the outputs when changing the link
state of the can interface or when resuming from suspend. Only if the
device is powered off during suspend it needs to be resetted as required
by the specs.

Signed-off-by: Timo Schlüßler <schluessler@krause.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>