drm/amdgpu: disallow multiple FENCE chunks in one submit

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

drm/amdgpu: disallow multiple FENCE chunks in one submit

amdgpu_cs_pass1() dispatches on chunk_id once per chunk without rejecting repeated ids. p->uf_bo is a single-slot field, so a submission carrying two AMDGPU_CHUNK_ID_FENCE chunks runs amdgpu_cs_p1_user_fence() twice, and the second run overwrites p->uf_bo with a freshly referenced BO without dropping the reference taken by the first.

amdgpu_cs_parser_fini() only unrefs the final p->uf_bo, so every FENCE chunk but the last leaks a BO reference. The leaked BO outlives handle close and process exit.

Reject duplicate FENCE chunks the same way commit fec5f8e8c6bc ("drm/amdgpu: disallow multiple BO_HANDLES chunks in one submit") did for p->bo_list.

(cherry picked from commit 665b1fc2a1845206408f9a2c6da67101789edb82)