drm/dsi: Use peripheral's channel for DCS commands

When executing DCS commands, use the channel associated with the DSI
peripheral rather than one explicitly specified in the function call.
Devices shouldn't be able to step on each others' toes like this.

Acked-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

include/drm/drm_mipi_dsi.h

@@ -127,10 +127,10 @@ struct mipi_dsi_device {
 
 int mipi_dsi_attach(struct mipi_dsi_device *dsi);
 int mipi_dsi_detach(struct mipi_dsi_device *dsi);
-ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, unsigned int channel,
-			   const void *data, size_t len);
-ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, unsigned int channel,
-			  u8 cmd, void *data, size_t len);
+ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
+			    size_t len);
+ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
+			  size_t len);
 
 /**
  * struct mipi_dsi_driver - DSI driver