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>