drm/amdgpu: Keep pending_reset valid during smu reset the ASIC

SMU internal might need to check this pending_reset setting to decide the reset method

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>