block, documentation: Sort queue sysfs attribute names alphabetically

Commit f9824952

 ("block: update sysfs documentation") # v5.0 broke the
alphabetical order of the sysfs attribute names. List queue sysfs attribute
names alphabetically.

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>