net: mediatek: mt7531/7988: fix broken PHY turn ON/OFF

net: mediatek: mt7531/7988: fix broken PHY turn ON/OFF

The PHY for MT7531/MT7988 are never actully turned ON/OFF for the
affected PHY as we are read/writing to the wrong PHY address.

This is caused by the fact that we use the MT753X_PHY_ADDR macro 2
times offsetting the address multiple times.

One in the _setup() function and one in the mt7531_mii_read/write.

Drop the additional usage of MT753X_PHY_ADDR in setup() to correctly
set the PHY.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>