drm/i915: Use correct downstream caps for check Src-Ctl mode for PCON

Fix the typo in DPCD caps used for checking SRC CTL mode of
HDMI2.1 PCON

v2: Corrected Fixes tag (Jani Nikula).
v3: Rebased.

Fixes: 04b6603d ("drm/i915/display: Configure HDMI2.1 Pcon for FRL only if Src-Ctl mode is available")

Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: "Ville Syrj_l_" <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210511120930.12218-1-ankit.k.nautiyal@intel.com
(cherry picked from commit 88a9c548)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

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

@@ -2111,7 +2111,7 @@ void intel_dp_check_frl_training(struct intel_dp *intel_dp)
 	 * -PCON supports SRC_CTL_MODE (VESA DP2.0-HDMI2.1 PCON Spec Draft-1 Sec-7)
 	 * -sink is HDMI2.1
 	 */
-	if (!(intel_dp->dpcd[2] & DP_PCON_SOURCE_CTL_MODE) ||
+	if (!(intel_dp->downstream_ports[2] & DP_PCON_SOURCE_CTL_MODE) ||
 	    !intel_dp_is_hdmi_2_1_sink(intel_dp) ||
 	    intel_dp->frl.is_trained)
 		return;