drm/nouveau: warn if we fail to re-pin fb on resume

Spotted by Coverity.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
index 1cc7b60..65b4fd5 100644
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -592,7 +592,9 @@
 		if (!nouveau_fb || !nouveau_fb->nvbo)
 			continue;
 
-		nouveau_bo_pin(nouveau_fb->nvbo, TTM_PL_FLAG_VRAM);
+		ret = nouveau_bo_pin(nouveau_fb->nvbo, TTM_PL_FLAG_VRAM);
+		if (ret)
+			NV_ERROR(drm, "Could not pin framebuffer\n");
 	}
 
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {