can: c_can_pci: c_can_pci_remove(): fix use-after-free

There is a UAF in c_can_pci_remove(). dev is released by
free_c_can_dev() and is used by pci_iounmap(pdev, priv->base) later.
To fix this issue, save the mmio address before releasing dev.

Fixes: 5b92da04

 ("c_can_pci: generic module for C_CAN/D_CAN on PCI")
Link: https://lore.kernel.org/r/20210301024512.539039-1-ztong0001@gmail.com
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>