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.

Fixes: 7f854420

 ("phy: Add API for {un}registering an mdio device to a bus.")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/cdf664ea-3312-e915-73f8-021678d08887@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>