drm/dsi: Constify mipi_dsi_msg

struct mipi_dsi_msg is a read-only structure, drivers should never need
to modify it. Make this explicit by making all references to the struct
const.

Acked-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/exynos/exynos_drm_dsi.c

@@ -1236,7 +1236,7 @@ static bool exynos_dsi_is_short_dsi_type(u8 type)
 }
 
 static ssize_t exynos_dsi_host_transfer(struct mipi_dsi_host *host,
-				       struct mipi_dsi_msg *msg)
+				        const struct mipi_dsi_msg *msg)
 {
 	struct exynos_dsi *dsi = host_to_dsi(host);
 	struct exynos_dsi_transfer xfer;

include/drm/drm_mipi_dsi.h

@@ -77,7 +77,7 @@ struct mipi_dsi_host_ops {
 	int (*detach)(struct mipi_dsi_host *host,
 		      struct mipi_dsi_device *dsi);
 	ssize_t (*transfer)(struct mipi_dsi_host *host,
-			    struct mipi_dsi_msg *msg);
+			    const struct mipi_dsi_msg *msg);
 };
 
 /**