btrfs: change dump_block_groups() in btrfs_dump_space_info() from int to bool

btrfs_dump_space_info()'s parameter dump_block_groups is used as a boolean
although it is defined as an integer.

Change it from int to bool.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Daniel Vacek <neelx@suse.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>