sis190: use an adequate phy list entry as a fallback

When sis190 driver is trying to get default phy, if it doesn't find home
or lan phy, it falls back to the first phy in the phy list but list_entry()
points to a bogus entry. list_first_entry() should be used instead.

Signed-off-by: Arnaud Patard <apatard@mandriva.com>
Acked-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>