sh_eth: remove 'tx_error_check' field of 'struct sh_eth_cpu_data'

The 'tx_error_check' field of 'struct sh_eth_cpu_data' is write-only, so remove
it along with the DEFAULT_TX_ERROR_CHECK macro.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>