nb/intel/*/graphic_init: use sizeof instead of hardcoding edid size

Change-Id: I2b8c4ef75cca9f9d5251789cda4187a02076b69d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/16964
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>

src/northbridge/intel/nehalem/gma.c

@@ -696,7 +696,8 @@ static void intel_gma_init(const struct northbridge_intel_nehalem_config *info,
 
 	power_port(mmio);
 
-	intel_gmbus_read_edid(mmio + PCH_GMBUS0, 3, 0x50, edid_data, 128);
+	intel_gmbus_read_edid(mmio + PCH_GMBUS0, 3, 0x50, edid_data,
+			sizeof(edid_data));
 	intel_gmbus_stop(mmio + PCH_GMBUS0);
 	decode_edid(edid_data,
 		    sizeof(edid_data), &edid);