kernel: block: Fix possible memory leak for rq_wb on add_disk failure

In the Linux kernel, the following vulnerability has been resolved: block: Fix possible memory leak for rqwb on adddisk failure kmemleak reported memory leaks in deviceadddisk: kmemleak: 3 new suspected memory leaks unreferenced object 0xffff88800f420800 size 512: comm "modprobe", pid 4275, jiffi...