net: sh_eth: fix endian check for architecture independent

SuperH has the "CONFIG_CPU_LITTLE_ENDIAN" and the "__LITTLE_ENDIAN__".
But, other architecture doesn't have them. So, this patch fixes it.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>