blktrace: fix blk_rq_merge documentation

The commit f3bdc62f ("blktrace: Provide event for request merging")
added the comment for blk_rq_merge() tracepoint. Remove the duplicate
word from the tracepoint documentation.

Fixes: f3bdc62f ("blktrace: Provide event for request merging")
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/trace/events/block.h

@@ -210,7 +210,7 @@ DEFINE_EVENT(block_rq, block_rq_issue,
 
 /**
  * block_rq_merge - merge request with another one in the elevator
- * @rq: block IO operation operation request
+ * @rq: block IO operation request
  *
  * Called when block operation request @rq from queue @q is merged to another
  * request queued in the elevator.