drm/amdgpu: Only clear dumb buffers if ring is enabled

	struct amdgpu_device *adev = dev->dev_private;

	struct drm_gem_object *gobj;

	uint32_t handle;

	u64 flags = AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;

	u32 domain;

	int r;

	/*

	 * The buffer returned from this function should be cleared, but

	 * it can only be done if the ring is enabled or we'll fail to

	 * create the buffer.

	 */

	if (adev->mman.buffer_funcs_enabled)

		flags |= AMDGPU_GEM_CREATE_VRAM_CLEARED;

	args->pitch = amdgpu_align_pitch(adev, args->width,

					 DIV_ROUND_UP(args->bpp, 8), 0);

	args->size = (u64)args->pitch * args->height;

	args->size = ALIGN(args->size, PAGE_SIZE);

	domain = amdgpu_bo_get_preferred_pin_domain(adev,

				amdgpu_display_supported_domains(adev));

	r = amdgpu_gem_object_create(adev, args->size, 0, domain,

				     AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED |

				     AMDGPU_GEM_CREATE_VRAM_CLEARED,

	r = amdgpu_gem_object_create(adev, args->size, 0, domain, flags,

				     ttm_bo_type_device, NULL, &gobj);

	if (r)

		return -ENOMEM;