drm/amdgpu: correct the amdgpu runtime dereference usage count

[ Upstream commit c6df7f31 ]

Fix the amdgpu runpm dereference usage count.

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>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>