Since 8ce8c0ab the driver queues work via priv->restart_work when
resuming after suspend, even when the interface was not previously
enabled. This causes a null dereference error as the workqueue is only
allocated and initialized in mcp251x_open().

To fix this we move the workqueue init to mcp251x_can_probe() as there
is no reason to do it later and repeat it whenever mcp251x_open() is
called.

Fixes: 8ce8c0ab ("can: mcp251x: only reset hardware as required")
Link: https://lore.kernel.org/r/17d5d714-b468-482f-f37a-482e3d6df84e@kontron.deSigned-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[mkl: fix error handling in mcp251x_stop()]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>