phylib: fix phy name example in documentation

All MDIO bus drivers currently name bus with "%x" format.
There is one exception where mv643xx_eth driver is using "%d".
Phy address on the bus uses format "%02x".

Fixing phy name example to match all real life MDIO drivers.

Signed-off-by: Paulius Zaleckas <paulius.zaleckas@teltonika.lt>
Signed-off-by: David S. Miller <davem@davemloft.net>