blk-mq: fix the cmd_flag_name array

Swap REQ_NOWAIT and REQ_NOUNMAP and add REQ_HIPRI.

Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>