block: remove duplicate BUG_ON() in bd_finish_claiming()

We do the same BUG_ON() just a line later when calling into
__bd_abort_claiming().

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

fs/block_dev.c

···
 				struct block_device *whole, void *holder)
 {
 	spin_lock(&bdev_lock);
-	BUG_ON(whole->bd_claiming != holder);
 	BUG_ON(!bd_may_claim(bdev, whole, holder));
 	__bd_claim(bdev, whole, holder);
 	__bd_abort_claiming(whole, holder); /* not actually an abort */