drm/amdgpu: disallow multiple FENCE chunks in one submit

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.

Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Assisted-by: Claude:claude-opus-5
Cc: stable@vger.kernel.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 665b1fc2a1845206408f9a2c6da67101789edb82)