net: enetc: do not skip setting LaBCR[MDIO_PHYAD_PRTAD] for addr 0

net: enetc: do not skip setting LaBCR[MDIO_PHYAD_PRTAD] for addr 0

Given that some platforms may use PHY address 0 (I suppose the PHY may
not treat address 0 as a broadcast address or default response address).
It is possible for some boards to connect multiple PHYs to the same
ENETC MAC, for example:

  - a PHY with a non-zero address connects to ENETC MAC through SGMII
    interface (selected via DTS_A)
  - a PHY with address 0 connects to ENETC MAC through RGMII interface
    (selected via DTS_B)

For the case where the ENETC port MDIO is used to manage the PHY, when
switching from DTS_A to DTS_B via soft reboot, LaBCR[MDIO_PHYAD_PRTAD]
must be updated to 0 because the NETCMIX block is not reset during soft
reboot. However, the current driver explicitly skips configuring address
0, causing LaBCR[MDIO_PHYAD_PRTAD] to retain its old value.

Therefore, remove the special-case skip of PHY address 0 so that valid
configurations using address 0 are properly supported.

Fixes: 6633df05f3ad ("net: enetc: set the external PHY address in IERB for port MDIO usage")
Fixes: 50bfd9c06f0f ("net: enetc: set external PHY address in IERB for i.MX94 ENETC")
Reviewed-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Link: https://patch.msgid.link/20260305031211.904812-3-wei.fang@nxp.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>