MAINTAINERS: PHY LIBRARY: Update files in the record

Update MAINTAINERS to reflect that sysfs-bus-mdio was removed in
commit a6cd0d2d ("Documentation: net-sysfs: Remove duplicate
PHY device documentation") and sysfs-class-net-phydev was added in
commit 86f22d04

 ("net: sysfs: Document PHY device sysfs
attributes").

Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Denis Efremov <efremov@linux.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>