crush: always return a value from crush_bucket_choose

Even when we encounter a corrupt bucket.  We still BUG().  This fixes
the warning

fs/ceph/crush/mapper.c: In function 'crush_choose':
fs/ceph/crush/mapper.c:352: warning: control may reach end of non-void function
'crush_bucket_choose' being inlined
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/crush/mapper.c

@@ -253,7 +253,7 @@ static int crush_bucket_choose(struct crush_bucket *in, int x, int r)
 					   x, r);
 	default:
 		BUG_ON(1);
-/* 		return in->items[0] */;
+ 		return in->items[0];
 	}
 }