net: phy: disable aneg in genphy_c45_pma_setup_forced

When genphy_c45_pma_setup_forced() is called the "aneg enabled" bit may
still be set, therefore clear it. This is also in line with what
genphy_setup_forced() does for Clause 22.

v2:
- fix typo

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>