ARM: dts: aspeed: AST2400 disables hw checksum

There is no need to specify this property in the device tree as the
AST2400 does not have working hardware checksum and disables it in the
driver.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Tao Ren <rentao.bupt@gmail.com>
Reviewed-by: Alexander Filippov <a.filippov@yadro.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>