btrfs: Fix bug for misused dev_t when lookup in dev state hash table.

Fix bug of commit 74d46992 ("block: replace bi_bdev with a gendisk
pointer and partitions index").

bio_dev(bio) is used to find the dev state in function
__btrfsic_submit_bio. But when dev_state is added to the hashtable, it
is using dev_t of block_device.

bio_dev(bio) returns a dev_t of part0 which is different from dev_t in
block_device(bd_dev). bd_dev in block_device represents the exact
partition.

block_device.bd_dev =
	bio->bi_partno (same as block_device.bd_partno) + bio_dev(bio).

When adding a dev_state into hashtable, we use the exact partition dev_t.
So when looking it up, it should also use the exact partition dev_t.

Reproducer of this bug:

Use MOUNT_OPTIONS="-o check_int" and run btrfs/001 in fstests.
Then there will be WARNING like below.

WARNING:
btrfs: attempt to write superblock which references block M @29523968 (sda7     /1111654400/2) which is never written!
Signed-off-by: Gu JinXiang <gujx@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/check-integrity.c

@@ -2803,7 +2803,7 @@ static void __btrfsic_submit_bio(struct bio *bio)
 	mutex_lock(&btrfsic_mutex);
 	/* since btrfsic_submit_bio() is also called before
 	 * btrfsic_mount(), this might return NULL */
-	dev_state = btrfsic_dev_state_lookup(bio_dev(bio));
+	dev_state = btrfsic_dev_state_lookup(bio_dev(bio) + bio->bi_partno);
 	if (NULL != dev_state &&
 	    (bio_op(bio) == REQ_OP_WRITE) && bio_has_data(bio)) {
 		unsigned int i = 0;