net: dsa: mxl862xx: don't set user_mii_bus

net: dsa: mxl862xx: don't set user_mii_bus

The PHY addresses in the MII bus are not equal to the port addresses,
so the bus cannot be assigned as user_mii_bus. Falling back on the
user_mii_bus in case a PHY isn't declared in device tree will result in
using the wrong (in this case: off-by-+1) PHY.
Remove the wrong assignment.

Fixes: 23794bec1cb60 ("net: dsa: add basic initial driver for MxL862xx switches")
Suggested-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/0f0df310fd8cab57e0e5e3d0831dd057fd05bcd5.1773103271.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>