btrfs: pass a struct reloc_control to prealloc_file_extent_cluster()

Pass a 'struct reloc_control' to prealloc_file_extent_cluster()
instead of passing its members 'data_inode' and 'cluster' on their own.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>