block: validate QoS before calling __rq_qos_done_bio()

If a bio has BIO_QOS_xxx set, it doesn't guarantee that q->rq_qos is
also present at-least for stacked block devices. For instance, in case
of NVMe when multipath is enabled, the bottom device may have QoS
enabled but top device doesn't. So always validate QoS is enabled and
q->rq_qos is present before calling __rq_qos_done_bio().

Fixes: 370ac285 ("block: avoid cpu_hotplug_lock depedency on freeze_lock")
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/all/3a07b752-06a4-4eee-b302-f4669feb859d@linux.ibm.com/


Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://lore.kernel.org/r/20250826163128.1952394-1-nilay@linux.ibm.com


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