drm/edid: Ignore "DFP 1.x" bit for EDID 1.2 and earlier

From VESA EDID implementation guide v1.0:
"For EDID version 1 revision 2 or earlier data structures when offset 14h
 bit 7 is set to one, the value of bits 6-0 are undefined, and therefore
 cannot be interpreted to mean anything."

And since EDID 1.4 redefines that bit let's consult it only for
EDID 1.3.

Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190529110204.2384-2-ville.syrjala@linux.intel.comReviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>

drivers/gpu/drm/drm_edid.c

@@ -4569,8 +4569,8 @@ u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edi
 	 * tells us to assume 8 bpc color depth if the EDID doesn't have
 	 * extensions which tell otherwise.
 	 */
-	if ((info->bpc == 0) && (edid->revision < 4) &&
-	    (edid->input & DRM_EDID_DIGITAL_DFP_1_X)) {
+	if (info->bpc == 0 && edid->revision == 3 &&
+	    edid->input & DRM_EDID_DIGITAL_DFP_1_X) {
 		info->bpc = 8;
 		DRM_DEBUG("%s: Assigning DFP sink color depth as %d bpc.\n",
 			  connector->name, info->bpc);