block/rnbd: Fix style issues

This patch fixes some style issues detected by scripts/checkpatch.pl
* Resolve spacing and tab issues
* Remove extra braces in rnbd_get_iu
* Use num_possible_cpus() instead of NR_CPUS in alloc_sess
* Fix the comments styling in rnbd_queue_rq

Signed-off-by: Dima Stepanov <dmitrii.stepanov@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20210428061359.206794-3-gi-oh.kim@ionos.com


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