block: export blk_verify_command for SG v4

blk_fill_sghdr_rq doesn't work for SG v4 so verify_command needed to
be exported.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 53002d4..f6bc0d0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -692,6 +692,7 @@
 extern int blk_unmap_sghdr_rq(struct request *, struct sg_io_hdr *);
 extern int blk_complete_sghdr_rq(struct request *, struct sg_io_hdr *,
 			  struct bio *);
+extern int blk_verify_command(unsigned char *, int);
 
 static inline request_queue_t *bdev_get_queue(struct block_device *bdev)
 {