tg3: negate USE_PHYLIB flag check

USE_PHYLIB flag in tg3_remove_one() is being checked incorrectly. This
results tg3_phy_fini->phy_disconnect is never called and when tg3 module
is removed.

In my case this resulted in panics in phy_state_machine calling function
phydev->adjust_link.

So correct this check.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Acked-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>