drm/amdgpu: Dereference the ATCS ACPI buffer

[ Upstream commit 32e7ee29 ]

Need to dereference the atcs acpi buffer after
the method is executed, otherwise it will result in
a memory leak.

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>