block: make nr_iovecs unsigned in bio_alloc_bioset()

There isn't a bug here, but Smatch is not smart enough to know that
"nr_iovecs" can't be negative so it complains about underflows.
Really, it's slightly cleaner to make this parameter unsigned.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8e52119..4931756 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -383,7 +383,7 @@ extern struct bio_set *bioset_create_nobvec(unsigned int, unsigned int);
 extern void bioset_free(struct bio_set *);
 extern mempool_t *biovec_create_pool(int pool_entries);
 
-extern struct bio *bio_alloc_bioset(gfp_t, int, struct bio_set *);
+extern struct bio *bio_alloc_bioset(gfp_t, unsigned int, struct bio_set *);
 extern void bio_put(struct bio *);
 
 extern void __bio_clone_fast(struct bio *, struct bio *);