Patch 
9667849bbb8d: "drm/amd/powerplay: add control gfxoff enabling in late
init" from Mar 13, 2018, leads to the following static checker warning:
	drivers/gpu/drm/amd/amdgpu/../powerplay/amd_powerplay.c:194
pp_late_init()
	error: we previously assumed 'hwmgr' could be null (see line 185)
drivers/gpu/drm/amd/amdgpu/../powerplay/amd_powerplay.c
This patch fixes the warning to add hwmgr checking.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
 
        if (adev->pm.smu_prv_buffer_size != 0)
                pp_reserve_vram_for_smu(adev);
 
-       if (hwmgr->hwmgr_func->gfx_off_control &&
+       if (hwmgr && hwmgr->hwmgr_func &&
+           hwmgr->hwmgr_func->gfx_off_control &&
            (hwmgr->feature_mask & PP_GFXOFF_MASK)) {
                ret = hwmgr->hwmgr_func->gfx_off_control(hwmgr, true);
                if (ret)