libethdrivers: Nitrogen6_SoloX imx6 driver seems to have mdio register access issue

I've found when trying to test imx6 ethernet driver on the Nitrogen6_SoloX platform that quite often, the mdio_read implementation (https://github.com/seL4/util_libs/blob/master/libethdrivers/src/plat/imx6/enet.c#L397) will start returning all ones (0xffff) until the hardware is reset.  Has anyone else experienced this or know what could cause this?