arm, imx, spi: detect spi flash again on aristainetos board

155fa9af95a "spi: mxc: fix sf probe when using mxc_spi" break
spi flash detection on the aristainetos board. Fix this.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/board/aristainetos/aristainetos.c b/board/aristainetos/aristainetos.c
index 3bfcf5b..06922c0 100644
--- a/board/aristainetos/aristainetos.c
+++ b/board/aristainetos/aristainetos.c
@@ -230,6 +230,12 @@
 	MX6_PAD_GPIO_2__GPIO1_IO02 | MUX_PAD_CTRL(NO_PAD_CTRL),
 };
 
+int board_spi_cs_gpio(unsigned bus, unsigned cs)
+{
+	return (bus == CONFIG_SF_DEFAULT_BUS && cs == CONFIG_SF_DEFAULT_CS)
+		? (IMX_GPIO_NR(3, 20)) : -1;
+}
+
 static void setup_spi(void)
 {
 	int i;