drm/bridge/synopsys: dsi: Fix dsi_host_transfer() return value

The dw_mipi_dsi_host_transfer() must return the number of
bytes transmitted/received on success instead of 0.
Note: As the read feature is not implemented, only the
transmitted number of bytes is returned for the moment.

Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180125103800.1999-3-philippe.cornu@st.com

drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c

@@ -412,7 +412,16 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
 
 	dw_mipi_message_config(dsi, msg);
 
-	return dw_mipi_dsi_write(dsi, &packet);
+	ret = dw_mipi_dsi_write(dsi, &packet);
+	if (ret)
+		return ret;
+
+	/*
+	 * TODO Only transmitted size is returned as actual driver does
+	 * not support dcs/generic reads. Please update return value when
+	 * delivering the read feature.
+	 */
+	return packet.size;
 }
 
 static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {