sis190: fix cable detect via link status poll

Some sis190 devices don't report LinkChange, so do polling for
link status.

Fixes http://bugzilla.kernel.org/show_bug.cgi?id=11926



Signed-off-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>
Signed-off-by: David S. Miller <davem@davemloft.net>