sh_eth: call sh_eth_tsu_write() from sh_eth_chip_reset_giga()

sh_eth_chip_reset_giga() doesn't really need to use direct iowrite32() when
writing  to the ARSTR register,  it can use sh_eth_tsu_write() as all other
chip_reset() methods.

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