net: phy: at803x: fix probe error if copper page is selected

The commit c329e5af ("net: phy: at803x: select correct page on
config init") selects the copper page during probe. This fails if the
copper page was already selected. In this case, the value of the copper
page (which is 1) is propagated through phy_restore_page() and is
finally returned for at803x_probe(). Fix it, by just using the
at803x_page_write() directly.

Also in case of an error, the regulator is not disabled and leads to a
WARN_ON() when the probe fails. This couldn't happen before, because
at803x_parse_dt() was the last call in at803x_probe(). It is hard to
see, that the parse_dt() actually enables the regulator. Thus move the
regulator_enable() to the probe function and undo it in case of an
error.

Fixes: c329e5af ("net: phy: at803x: select correct page on config init")
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: David Bauer <mail@david-bauer.net>
Signed-off-by: David S. Miller <davem@davemloft.net>