smsc911x: Remove dev==NULL check.

The dev==NULL check in smsc911x_probe_config is useless
and isn't providing any additional protection. If a fwnode
doesn't exist then an appropriate error should be returned
by device_get_phy_mode() covering the original case
of a missing of/fwnode.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>