net: dsa: probe master device

DSA needs to have the master device probed first for MAC inheritance.
Until now, it only works by chance because the only user (LS1028A SoC)
will probe the master device first. The probe order is given by the PCI
device ordering, thus it works because the master device has a "smaller"
BDF then the switch device.

Explicitly probe the master device in dsa_port_probe().

Fixes: fc054d56 ("net: Introduce DSA class for Ethernet switches")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>