net: mvpp2: initialize port fwnode pointer

Update the port's device structure also with its fwnode pointer
with a recommended device_set_node() helper routine.

Signed-off-by: Marcin Wojtas <marcin.s.wojtas@gmail.com>
Reviewed-by: Suman Ghosh <sumang@marvell.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20231231122019.123344-1-marcin.s.wojtas@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>