can: bfin_can: auto-calculate accessor sizes

Since we have a struct that defines the sizes of the registers, we don't
need to explicitly use the 16bit read/write helpers.  Let the code figure
out which size access to make based on the size of the C type.

There should be no functional changes here.

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