net: phylink: fix regression when binding a PHY

Some PHYs don't support clause 45 access, and return -EOPNOTSUPP from
phy_modify_mmd(), which causes phylink_bringup_phy() to fail. Prevent
this failure by allowing -EOPNOTSUPP to also mean success.

Reported-by: Jiawen Wu <jiawenwu@trustnetic.com>
Tested-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/E1tZp1a-001V62-DT@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>