Use phy_find_first() to find the first phy device instead of
open coding it.

Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Acked-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>