blk-rq-qos: Remove unlikely() hints from QoS checks

blk-rq-qos: Remove unlikely() hints from QoS checks

The unlikely() annotations on QUEUE_FLAG_QOS_ENABLED checks are
counterproductive. Writeback throttling (WBT) might be enabled by
default, mainly because CONFIG_BLK_WBT_MQ defaults to 'y'.

Branch profiling on Meta servers, which have WBT enabled, confirms 100%
misprediction rates on these checks.

Remove the unlikely() annotations to let the CPU's branch predictor
learn the actual behavior, potentially improving I/O path performance.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>