net: mdio_bus: validate "addr" for mdiobus_is_registered_device()

mdiobus_is_registered_device() doesn't checking that "addr" was valid
before dereferencing bus->mdio_map[]. Extract the code that checks
this from mdiobus_get_phy(), and use it here as well.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/E1qNxvu-00111m-1V@rmk-PC.armlinux.org.ukSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/phy/mdio_bus.c

@@ -107,16 +107,21 @@ int mdiobus_unregister_device(struct mdio_device *mdiodev)
 }
 EXPORT_SYMBOL(mdiobus_unregister_device);
 
-struct phy_device *mdiobus_get_phy(struct mii_bus *bus, int addr)
+static struct mdio_device *mdiobus_find_device(struct mii_bus *bus, int addr)
 {
 	bool addr_valid = addr >= 0 && addr < ARRAY_SIZE(bus->mdio_map);
-	struct mdio_device *mdiodev;
 
 	if (WARN_ONCE(!addr_valid, "addr %d out of range\n", addr))
 		return NULL;
 
-	mdiodev = bus->mdio_map[addr];
+	return bus->mdio_map[addr];
+}
 
+struct phy_device *mdiobus_get_phy(struct mii_bus *bus, int addr)
+{
+	struct mdio_device *mdiodev;
+
+	mdiodev = mdiobus_find_device(bus, addr);
 	if (!mdiodev)
 		return NULL;
 
@@ -129,7 +134,7 @@ EXPORT_SYMBOL(mdiobus_get_phy);
 
 bool mdiobus_is_registered_device(struct mii_bus *bus, int addr)
 {
-	return bus->mdio_map[addr];
+	return mdiobus_find_device(bus, addr) != NULL;
 }
 EXPORT_SYMBOL(mdiobus_is_registered_device);