can: fix bfin_can build error after alloc_candev() change

Looks like commit a6e4bc53

 didn't include updates to drivers so the
Blackfin CAN driver fails to build now.

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