SiS190/191 half-duplex initialization fix

Adds half-duplex specific setup code (taken from SiS own GPL driver).
Without those, half-duplex connections are very unreliable, often
working on small transfers and failing after a while.

Signed-off-by: Riccardo Ghetta <birrachiara@tin.it>
Signed-off-by: David S. Miller <davem@davemloft.net>