net: usb: asix: ax88772: do not poll for PHY before registering it

asix_get_phyid() is used for two reasons here. To print debug message
with the PHY ID and to wait until the PHY is powered up.

After migrating to the phylib, we can read PHYID from sysfs. If polling
for the PHY is really needed, then we will need to handle it in the
phylib as well.

This change was tested with:
- ax88772a + internal PHY
- ax88772b + external PHY

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>