drm/panthor: avoid garbage value in panthor_ioctl_dev_query()

In the Linux kernel, the following vulnerability has been resolved: drm/panthor: avoid garbage value in panthor_ioctl_dev_query() 'priorities_info' is uninitialized, and the uninitialized value is copied to user object when calling PANTHOR_UOBJ_SET(). Using memset to initialize 'priorities_info' to avoid this garbage value problem.