arm: mvebu: a38x: Call bb_miiphy init directly in driver probe

arm: mvebu: a38x: Call bb_miiphy init directly in driver probe

All the resources needed by this .init callback should already
be available by the time probe function runs, simply call the
init callback directly and set the bb_miiphy init callback to
NULL. This shouldn't break anything on this hardware, but would
be nice if someone could double-check and test that.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>