drm/amdgpu: Handling of amdgpu_device_resume return value for graceful teardown

The runtime resume PM op disregards the return value from
amdgpu_device_resume(), masking errors for failed resumes at the PM
layer.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Pavan Kumar Ramayanam <pavan.ramayanam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>