drm/amdgpu: fix ras UE error injection failure issue

The ras command shared memory is allocated from
VRAM and the response status of the command
buffer will not be zero due to gpu being in
fatal error state after ras UE error injection.

Signed-off-by: YiPeng Chai <YiPeng.Chai@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>