8139x: reduce message severity on driver overlap

The 8139 drivers are a source of error messages that confuse users.

Since this device can not be disambiguated by normal PCI device
id's two drivers match the same info. But the module utilities
seem to correctly handle this overlap, they try one driver, then
if that doesn't load try the other. Therefore there is no need for
a message to be logged with error level severity, just using info
level instead. Can't be completely silent because user might have
configure one driver and forgot the other one.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>