Without "fix" I have the same result:
root@OpenWrt:/# mdio 9* mmd 8:4 0xC441
0x0000
root@OpenWrt:/# mdio 9* mmd 8:4 0xC441 8
root@OpenWrt:/# mdio 9* mmd 8:4 0xC441
0x0008
[ 603.112186] nss-dp 3a007000.dp6-syn wan: PHY Link up speed: 100
Maybe the changes mentioned by @rmandrad are needed: Adding OpenWrt support for QNAP QHora-301W - #749 by rmandrad ?