drm/amdgpu: Validate bo_count alignment

Even though bo_count is derived from the length, the offset must still be checked for alignment.

Signed-off-by: Demi Marie Obenour demi@invisiblethingslab.com Fixes: 8fad50f8 (drm/amdgpu: remove amdgpu_ccmd_cs_submit_req::bo_number)