fsl/fman: Save device references taken in mac_probe()

In mac_probe() there are calls to of_find_device_by_node() which takes
references to of_dev->dev. These references are not saved and not released
later on error path in mac_probe() and in mac_remove().

Add new fields into mac_device structure to save references taken for
future use in mac_probe() and mac_remove().

This is a preparation for further reference leaks fix.

Signed-off-by: Aleksandr Mishin <amishin@t-argos.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>