modules/partdisks/front/glade: automatic_calc(): when setting up self.changed in order to switch to the manual summary scene, properly store the device and disk objects.

self.changed[diskpath]["obj"] was a Disk object, instead of a Device. Disks should be associated with the "disk" key.
This broke the automatic mode after 77371d5fcd043fd7685f486795027796105519d5, as manual_frame_creator() now expects a Device object (to retrieve its path).
This commit should also fix the intermittent issues with the automatic partitioner.
Thanks again to Filip Danilovic for the bug report.