can: c_can_pci: fix null-pointer-deref in c_can_start() - set device pointer

The priv->device pointer for c_can_pci is never set, but it is used
without a NULL check in c_can_start(). Setting it in c_can_pci_probe()
like c_can_plat_probe() prevents c_can_pci.ko from crashing, with and
without CONFIG_PM.

This might also cause the pm_runtime_*() functions in c_can.c to
actually be executed for c_can_pci devices - they are the only other
place where priv->device is used, but they all contain a null check.

Signed-off-by: Einar Jón <tolvupostur@gmail.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>