net/phy: micrel: Comment MMD address of extended registers

There are some defines for a few pad skew related extended registers.
Specify for which MMD Address (dev_addr) they are for.
Signed-off-by: NJaeden Amero <jaeden.amero@ni.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/micrel.c

@@ -366,6 +366,7 @@ static int ksz9021_config_init(struct phy_device *phydev)
 #define KSZ9031_PS_TO_REG		60
 
 /* Extended registers */
+/* MMD Address 0x2 */
 #define MII_KSZ9031RN_CONTROL_PAD_SKEW	4
 #define MII_KSZ9031RN_RX_DATA_PAD_SKEW	5
 #define MII_KSZ9031RN_TX_DATA_PAD_SKEW	6