Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f7/STM32F767/MDIOS/MDIOS_RDFR#0x0
MDIOS read flag register
Read flags for MDIO registers 0 to 31
https://github.com/modm-io/cmsis-svd-stm32