Add error handling from calling fixed_phy_register.
It may return some error, therefore, need to check the status.

And fixed_phy_register needs to bind a device node for mdio.
Add the mac device node for fixed_phy_register function.
This is a reference to this function, of_phy_register_fixed_link().

Fixes: e24a6c87 ("net: ftgmac100: Get link speed and duplex for NC-SI")
Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
Link: https://patch.msgid.link/20241007032435.787892-1-jacky_chou@aspeedtech.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>