drm/amdgpu/cik: don't mess with aspm if gpu is root bus

BugLink: http://bugs.launchpad.net/bugs/1546572

Pcie registers may not be available in a virtualized
environment.
Reviewed-by: monk liu <monk.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 76ecb2c7)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/cik.c

@@ -1762,6 +1762,9 @@ static void cik_program_aspm(struct amdgpu_device *adev)
 	if (amdgpu_aspm == 0)
 		return;
 
+	if (pci_is_root_bus(adev->pdev->bus))
+		return;
+
 	/* XXX double check APUs */
 	if (adev->flags & AMD_IS_APU)
 		return;