sis190: read the mac address from the eeprom first

Reading a serie of zero from the cmos sram area do not work
well with is_valid_ether_addr(). Let's read the mac address
from the eeprom first as it seems more reliable.

Fix for http://bugzilla.kernel.org/show_bug.cgi?id=9831

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>