Don't define empty struct bsg_class_device if !CONFIG_BLK_DEV_BSG

Don't define an empty struct bsg_class_device if !CONFIG_BLK_DEV_BSG.

It's embedded in struct request_queue, but there we have

#if defined(CONFIG_BLK_DEV_BSG)
	struct bsg_class_device bsg_dev;
#endif

anyway.
Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/bsg.h

@@ -60,7 +60,6 @@ struct bsg_class_device {
 extern int bsg_register_queue(struct request_queue *, const char *);
 extern void bsg_unregister_queue(struct request_queue *);
 #else
-struct bsg_class_device { };
 #define bsg_register_queue(disk, name)		(0)
 #define bsg_unregister_queue(disk)	do { } while (0)
 #endif