blk-throttle: Make total_nr_queued unsigned

The total of two unsigned values should also be unsigned.

Update throtl_log output to unsigned.
Update total_nr_queued test to non-zero to be the
same as the other total_nr_queued tests.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>