libtracker-miner: fix thinko in TrackerFileNotifier
libtracker-miner: fix thinko in TrackerFileNotifier

"canonical" was supposed to be the root dir as configured in
the indexing tree, so the if below forces mtime checks on
directories that do come from TrackerMonitor signals. so rename
it to something sensible and actually initialize it.

outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker