mq-deadline: Remove a local variable

Since commit fde02699 ("block: mq-deadline: Remove support for zone
write locking"), the local variable 'insert_before' is assigned once and
is used once. Hence remove this local variable.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nitesh Shetty <nj.shetty@samsung.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20241212212941.1268662-2-bvanassche@acm.org


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