doc: Fix typo in request queue sysfs documentation

Fix a typo (are -> as) in the introduction paragraph of
Documentation/block/queue-sysfs.rst.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20211027022223.183838-6-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Documentation/block/queue-sysfs.rst

@@ -4,7 +4,7 @@ Queue sysfs files
 
 This text file will detail the queue files that are located in the sysfs tree
 for each block device. Note that stacked devices typically do not export
-any settings, since their queue merely functions are a remapping target.
+any settings, since their queue merely functions as a remapping target.
 These files are the ones found in the /sys/block/xxx/queue/ directory.
 
 Files denoted with a RO postfix are readonly and the RW postfix means