drm/amd/pm: Init pm_attr_list when dpm is disabled

[Why]
In SRIOV multi-vf, dpm is always disabled, and pm_attr_list won't
be initialized. There will be a NULL pointer call trace after
removing the dpm check condition in amdgpu_pm_sysfs_fini.
BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:amdgpu_device_attr_remove_groups+0x20/0x90 [amdgpu]
Call Trace:
<TASK>
amdgpu_pm_sysfs_fini+0x2f/0x40 [amdgpu]
amdgpu_device_fini_hw+0xdf/0x290 [amdgpu]

[How]
List pm_attr_list should be initialized when dpm is disabled.

Fixes: a6ad27cec585fe ("drm/amd/pm: Remove redundant check condition")
Signed-off-by: ZhenGuo Yin <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/pm/amdgpu_pm.c

···
 	if (adev->pm.sysfs_initialized)
 		return 0;
 
+	INIT_LIST_HEAD(&adev->pm.pm_attr_list);
+
 	if (adev->pm.dpm_enabled == 0)
 		return 0;
-
-	INIT_LIST_HEAD(&adev->pm.pm_attr_list);
 
 	adev->pm.int_hwmon_dev = hwmon_device_register_with_groups(adev->dev,
 								   DRIVER_NAME, adev,