sh_eth: make sh_eth_tsu_write_entry() take 'offset' parameter

We can add the TSU register base address to a TSU register offset right
in sh_eth_tsu_write_entry(),  no need to do it in its callers...

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