net: phy: convert micrel to new read_mmd/write_mmd driver methods

Convert micrel to the new read_mmd/write_mmd driver methods.  This
Clause 22 PHY does not support any MMD access method.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>