drm/amdgpu: Use a different value than 0xDEADBEEF for jpeg ring test

The 0xDEADBEEF standard anti-hang value. Use it may cause
fake pass.

Signed-off-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>