drm/edid: Only parse VRR range for continuous frequency displays

Since we only use the parsed vrefresh range to determine
if VRR should be supported we should only accept continuous
frequency displays here.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220927170006.27855-4-ville.syrjala@linux.intel.com