lib/edid.c: Differentiate between absent and non-conformant EDID

Change-Id: Id90aa210ff72092c4ab638a7bafb82bd11889bdc
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19502
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/drivers/parade/ps8640/ps8640.c

@@ -47,7 +47,7 @@ int ps8640_get_edid(uint8_t bus, uint8_t chip, struct edid *out)
 		}
 	}
 
-	if (decode_edid(edid, edid_size, out)) {
+	if (decode_edid(edid, edid_size, out) != EDID_CONFORMANT) {
 		printk(BIOS_INFO, "Failed to decode EDID.\n");
 		return -1;
 	}