drm/nouveau: Fix bandwidth calculation for DisplayPort

Ported from the equivalent fix in drm-intel-next:

http://cgit.freedesktop.org/~keithp/linux/commit/?h=drm-intel-next&id=cd9dde44f47501394b9f0715b6a36a92aa74c0d0Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_connector.c

@@ -710,7 +710,7 @@ nouveau_connector_mode_valid(struct drm_connector *connector,
 	case OUTPUT_DP:
 		max_clock  = nv_encoder->dp.link_nr;
 		max_clock *= nv_encoder->dp.link_bw;
-		clock = clock * nouveau_connector_bpp(connector) / 8;
+		clock = clock * nouveau_connector_bpp(connector) / 10;
 		break;
 	default:
 		BUG_ON(1);