net: dsa: felix: remove felix_info :: imdio_res

The imdio_res is used only by vsc9959, which references its own
vsc9959_imdio_res through the common felix_info->imdio_res pointer.
Since the common code doesn't care about this resource (and it can't be
part of the common array of resources, either, because it belongs in a
different PCI BAR), just reference it directly.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>