gpu: drm: replace of_graph_get_next_endpoint()

From DT point of view, in general, drivers should be asking for a
specific port number because their function is fixed in the binding.

of_graph_get_next_endpoint() doesn't match to this concept.

Simply replace

- of_graph_get_next_endpoint(xxx, NULL);
+ of_graph_get_endpoint_by_regs(xxx, 0, -1);

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Kuninori Morimoto <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Reviewed-by: Dmitry Baryshkov <[e-mail]>
Signed-off-by: Thomas Zimmermann <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_of.c

···
  * Gets parent DSI bus for a DSI device controlled through a bus other
  * than MIPI-DCS (SPI, I2C, etc.) using the Device Tree.
  *
+ * This function assumes that the device's port@0 is the DSI input.
+ *
  * Returns pointer to mipi_dsi_host if successful, -EINVAL if the
  * request is unsupported, -EPROBE_DEFER if the DSI host is found but
  * not available, or -ENODEV otherwise.
···
 	/*
 	 * Get first endpoint child from device.
 	 */
-	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
+	endpoint = of_graph_get_endpoint_by_regs(dev->of_node, 0, -1);
 	if (!endpoint)
 		return ERR_PTR(-ENODEV);
 

drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c

···
 	rpi_touchscreen_i2c_write(ts, REG_POWERON, 0);
 
 	/* Look up the DSI host.  It needs to probe before we do. */
-	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
+	endpoint = of_graph_get_endpoint_by_regs(dev->of_node, 0, -1);
 	if (!endpoint)
 		return -ENODEV;
 

drivers/gpu/drm/tiny/arcpgu.c

···
 	 * There is only one output port inside each device. It is linked with
 	 * encoder endpoint.
 	 */
-	endpoint_node = of_graph_get_next_endpoint(pdev->dev.of_node, NULL);
+	endpoint_node = of_graph_get_endpoint_by_regs(pdev->dev.of_node, 0, -1);
 	if (endpoint_node) {
 		encoder_node = of_graph_get_remote_port_parent(endpoint_node);
 		of_node_put(endpoint_node);