drm/amdgpu: don't access invalid sched

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: don't access invalid sched Since 2320c9e6a768 ("drm/sched: memset() 'job' in drm_sched_job_init()") accessing job->base.sched can produce unexpected results as the initialisation of (*job)->base.sched done in amdgpu_job_alloc is overwritten by the memset. This commit fixes an issue when a CS would fail validation and would be rejected after job->num_ibs is incremented. In this case, amdgpu_ib_free(ring->adev, ...) will be called, which would crash the machine because the ring value is bogus. To fix this, pass a NULL pointer to amdgpu_ib_free(): we can do this because the device is actually not used in this function. The next commit will remove the ring argument completely. (cherry picked from commit 2ae520cb12831d264ceb97c61f72c59d33c0dbd7)