can: sja1000: stop misusing member base_addr of struct net_device

As discussed on the netdev mailing list, the member "base_addr" of
"struct net_device" should not be (mis)used to store the virtual
address to the SJA1000 register area. According to David Miller,
it's only use is to allow ISA and similar primitive bus devices to
have their I/O ports changed via ifconfig. The virtual address is
now stored in the private data structure of the SJA1000 device and
the callback functions use "struct sja1000_priv" instead of the
unneeded "struct net_device".

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>