loop: remove unused variable in loop_set_status()

Commit 0384264e ("block: pass a gendisk to bdev_disk_changed")
changed to pass lo->lo_disk instead of lo->lo_device.

Fixes: 0384264e ("block: pass a gendisk to bdev_disk_changed")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/20210702152714.7978-1-penguin-kernel@I-love.SAKURA.ne.jp


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