sh_eth: uninline sh_eth_tsu_get_offset()

sh_eth_tsu_get_offset() is called several  times  by the driver, remove
*inline* and move  that function  from the header to the driver  itself
to let gcc decide  whether to expand it inline or not...

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