net: mdio: validate parameter addr in mdiobus_get_phy()

In the Linux kernel, the following vulnerability has been resolved: net: mdio: validate parameter addr in mdiobus_get_phy() The caller may pass any value as addr, what may result in an out-of-bounds access to array mdio_map. One existing case is stmmac_init_phy() that may pass -1 as addr. Therefore validate addr before using it.