drm: Constify adjusted_mode a bit

The DP link computation functions shouldn't modify the
adjusted_mode so make it const.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200319163844.22783-3-ville.syrjala@linux.intel.comReviewed-by: NManasi Navare <manasi.d.navare@intel.com>

drivers/gpu/drm/i915/display/intel_dp.c

@@ -2125,7 +2125,8 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
-	struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
+	const struct drm_display_mode *adjusted_mode =
+		&pipe_config->hw.adjusted_mode;
 	u8 dsc_max_bpc;
 	int pipe_bpp;
 	int ret;
@@ -2240,7 +2241,8 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config,
 			     struct drm_connector_state *conn_state)
 {
-	struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
+	const struct drm_display_mode *adjusted_mode =
+		&pipe_config->hw.adjusted_mode;
 	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
 	struct link_config_limits limits;
 	int common_len;