drm/amdgpu/pm: Fix uninitialized variable agc_btc_response

[ Upstream commit df4409d8 ]

Assign an default value to agc_btc_response in failed case

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>