This fixes the following warnings:

    ../src/miners/fs/tracker-miner-files.c: In function ‘miner_files_process_file’:
    ../src/miners/fs/tracker-miner-files.c:2502:14: warning: assignment to ‘TrackerMinerFiles *’ {aka ‘struct TrackerMinerFiles *’} from incompatible pointer type ‘TrackerMinerFS *’ {aka ‘struct _TrackerMinerFS *’} [-Wincompatible-pointer-types]
      data->miner = g_object_ref (fs);
                  ^
    ../src/miners/fs/tracker-miner-files.c: In function ‘miner_files_process_file_attributes’:
    ../src/miners/fs/tracker-miner-files.c:2604:14: warning: assignment to ‘TrackerMinerFiles *’ {aka ‘struct TrackerMinerFiles *’} from incompatible pointer type ‘TrackerMinerFS *’ {aka ‘struct _TrackerMinerFS *’} [-Wincompatible-pointer-types]
      data->miner = g_object_ref (fs);