fs: bdev: fix conflicting comment from lookup_bdev

We switched to directly use dev_t to get block device, lookup changed the
meaning of use, now we fix this conflicting comment.

Fixes: 4e7b5671 ("block: remove i_bdev")
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211021071344.1600362-1-liu.yun@linux.devSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bdev.c

@@ -964,9 +964,11 @@ EXPORT_SYMBOL(blkdev_put);
  * @pathname:	special file representing the block device
  * @dev:	return value of the block device's dev_t
  *
- * Get a reference to the blockdevice at @pathname in the current
- * namespace if possible and return it.  Return ERR_PTR(error)
- * otherwise.
+ * Lookup the block device's dev_t at @pathname in the current
+ * namespace if possible and return it by @dev.
+ *
+ * RETURNS:
+ * 0 if succeeded, errno otherwise.
  */
 int lookup_bdev(const char *pathname, dev_t *dev)
 {