can: bfin_can: switch to common Blackfin can header

The MMR bits are being moved to this header, so include it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>