drm/amd/powerplay: Fix potential NULL pointer issue

If doesn't enable dpm, the powerplay will not allocate memory for
hw management. So, hw_init_power_state_table function will reference
NULL pointer when resetting.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org