block: document the holder argument to blkdev_get_by_path

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230620043536.707249-1-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bdev.c

@@ -850,6 +850,7 @@ EXPORT_SYMBOL(blkdev_get_by_dev);
  * @path: path to the block device to open
  * @mode: open mode (BLK_OPEN_*)
  * @holder: exclusive holder identifier
+ * @hops: holder operations
  *
  * Open the block device described by the device file at @path.  If @holder is
  * not %NULL, the block device is opened with exclusive access.  Exclusive opens