drm/stm: dsi: Constify phy ops structure

Constify dw_mipi_dsi_stm_phy_ops as these ops are not supposed
to change at runtime.
Signed-off-by: Philippe CORNU <philippe.cornu@st.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1500552357-29487-8-git-send-email-philippe.cornu@st.com

drivers/gpu/drm/stm/dw_mipi_dsi-stm.c

@@ -261,7 +261,7 @@ dw_mipi_dsi_get_lane_mbps(void *priv_data, struct drm_display_mode *mode,
 	return 0;
 }
 
-static struct dw_mipi_dsi_phy_ops dw_mipi_dsi_stm_phy_ops = {
+static const struct dw_mipi_dsi_phy_ops dw_mipi_dsi_stm_phy_ops = {
 	.init = dw_mipi_dsi_phy_init,
 	.get_lane_mbps = dw_mipi_dsi_get_lane_mbps,
 };