google/jecht: fix MAC address programming when VPD not present

Fix by checking the actual function return value (the search
address pointer), rather than the search length value (which isn't
guaranteed to be sane or useful).

Change-Id: I226c635ddbbc916b02494fcd97df27d141cc2c7f
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: http://review.coreboot.org/10516
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/mainboard/google/jecht/lan.c

@@ -132,7 +132,7 @@ static void program_mac_address(u16 io_base)
 							&search_length);
 	}
 
-	if (search_length <= 0)
+	if (search_address == NULL)
 		printk(BIOS_ERR, "LAN: VPD not found.\n");
 	else
 		get_mac_address(&high_dword, &low_dword, search_address,