build: Fix error message when running configure for tracker-miner-fs
build: Fix error message when running configure for tracker-miner-fs

Bad spacing on variable assignment caused an error message:
"enable_tracker_miner_fs: command not found"

https://bugzilla.gnome.org/show_bug.cgi?id=726552

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