CVE-2023-53498

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix potential null dereference

The adev->dm.dc pointer can be NULL and dereferenced in amdgpu_dm_fini()
without checking.

Add a NULL pointer check before calling dc_dmub_srv_destroy().

Found by Linux Verification Center (linuxtesting.org) with SVACE.