CVE-2023-54087 ubi: Fix possible null-ptr-deref in ubi_free_volume()

In the Linux kernel, the following vulnerability has been resolved: ubi: Fix possible null-ptr-deref in ubifreevolume It willl cause null-ptr-deref in the following case: uifinit ubiaddvolume cdevadd - if it fails, call killvolumes deviceregister killvolumes - if ubiaddvolume fails call this...