[BLOCK] bio: init ->bi_bdev in bio_init()

For SG_IO requests, bio->bi_bdev may not be explicitly initialized. So make
bio_init() clear the field to make sure it's always NULL or valid.

Signed-off-by: Jens Axboe <[e-mail]>

fs/bio.c

···
 inline void bio_init(struct bio *bio)
 {
 	bio->bi_next = NULL;
+	bio->bi_bdev = NULL;
 	bio->bi_flags = 1 << BIO_UPTODATE;
 	bio->bi_rw = 0;
 	bio->bi_vcnt = 0;