CVE-2026-68251 drm/amdgpu/sdma6.0: replace BUG_ON() with WARN_ON()

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu/sdma6.0: replace BUGON with WARNON There's no need to crash the kernel for these cases. cherry picked from commit c17a508a7d652da3728f8bbc481bfffe96d65a87...