drm/amdgpu: Add missing pm_runtime_put_autosuspend

pm_runtime_get_sync() increments the runtime PM usage counter even
when it returns an error code, thus a matching decrement is needed
on the error handling path to keep the counter balanced.

Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>