net: dpaa2-mac: allow lynx PCS to manage mdiodev lifetime

Put the mdiodev after lynx_pcs_create() so that the Lynx PCS driver
can manage the lifetime of the mdiodev its using.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>