blk-cgroup: always terminate io.stat lines

With the removal of seq_get_buf in blkcg_print_one_stat, we
cannot make adding the newline conditional on there being
relevant stats because the name was already written out
unconditionally.
Otherwise we may end up with multiple device names in one
line which is confusing and doesn't follow the nested-keyed
file format.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Fixes: 252c651a ("blk-cgroup: stop using seq_get_buf")
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220111083159.42340-1-w.bumiller@proxmox.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>