drm/radeon: use the dummy page for GART if needed

Imported BOs don't have a pagelist any more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Fixes: 0575ff3 ("drm/radeon: stop using pages with drm_prime_sg_to_page_addr_arrays v2")
CC: stable@vger.kernel.org # 5.12

drivers/gpu/drm/radeon/radeon_gart.c

@@ -301,7 +301,8 @@ int radeon_gart_bind(struct radeon_device *rdev, unsigned offset,
 	p = t / (PAGE_SIZE / RADEON_GPU_PAGE_SIZE);
 
 	for (i = 0; i < pages; i++, p++) {
-		rdev->gart.pages[p] = pagelist[i];
+		rdev->gart.pages[p] = pagelist ? pagelist[i] :
+			rdev->dummy_page.page;
 		page_base = dma_addr[i];
 		for (j = 0; j < (PAGE_SIZE / RADEON_GPU_PAGE_SIZE); j++, t++) {
 			page_entry = radeon_gart_get_page_entry(page_base, flags);