drm/amdgpu: exit directly if gpu reset fails

No need to perform the full reset operation in case of gpu reset
failure.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>