drm/amdgpu/pm: Fix the null pointer dereference in apply_state_adjust_rules

[ Upstream commit d19fb100 ]

Check the pointer value to fix potential null pointer
dereference

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