Fix new generic block device SG compile

We had a merge issue with the "dentry" field going away from the
kobject, and being replaced by a sysfs_dirent field (named "sd")
instead.  That broke the BSG compile.

Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: James Bottomley <James.Bottomley@SteelEye.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

block/bsg.c

@@ -1011,7 +1011,7 @@ int bsg_register_queue(struct request_queue *q, const char *name)
 	}
 	bcd->class_dev = class_dev;
 
-	if (q->kobj.dentry) {
+	if (q->kobj.sd) {
 		ret = sysfs_create_link(&q->kobj, &bcd->class_dev->kobj, "bsg");
 		if (ret)
 			goto err;