backends/drm: make DrmObject::updateProperties handle data races better
The kernel sometimes changes blob IDs in the middle of us parsing the properties. In order to make this less likely to happen, fetch the properties more often.
The time difference between checking the properties is super minimal, but changing when blobs were read changed things last time as well. This is also how wlroots is parsing the properties, and they don't seem to have problems with these data races... so it's worth a shot