nwl-dsi: Save correct tx_len

Length is shortened in the above loop but we want the total amount of
bytes to transfer since this is reported back later on to the caller of
mipi_dsi_host's (*transfer)() via xfer.status.
Signed-off-by: Guido Günther <guido.gunther@puri.sm>

drivers/gpu/drm/bridge/nwl-dsi.c

@@ -782,7 +782,7 @@ static void nwl_dsi_begin_transmission(struct nwl_mipi_dsi *dsi)
 		nwl_dsi_write(dsi, TX_PAYLOAD, val);
 		break;
 	}
-	xfer->tx_len = length;
+	xfer->tx_len = pkt->payload_length;
 
 	/*
 	 * Now, send the header