Before calling blk_mq_map_queues(), the mq_map and nr_queues belonging to
struct blk_mq_queue_map must have a valid value.

If nr_queues is set to 0, the system may encounter a divide by zero
depending on the type of architecture.

    blk_mq_map_queues() -> queue_index()

Link: https://lore.kernel.org/r/1891546521.01644873481638.JavaMail.epsvc@epcpadp4Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jinyoung Choi <j-young.choi@samsung.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>