sunhme: switch to devres

This not only removes a lot of code, it also fixes the memleak of the DMA
memory when register_netdev() fails.

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
[ rebased onto net-next/master; fixed error reporting ]
Signed-off-by: Sean Anderson <seanga2@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>