ARM: shmobile: lager: Do not use register_type field of struct sh_eth_plat_data

As of 8d3214c4

 ("sh_eth: remove 'register_type' field from 'struct
sh_eth_plat_data'") is is no longer necessary or correct to use the
'register_type' field from 'struct sh_eth_plat_data' and doing so results
in a build error.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Olof Johansson <olof@lixom.net>