ARM: at91/boards: use -EINVAL for invalid gpio

this will allow to use gpio_is_valid

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/mach-at91/board-dt.c b/arch/arm/mach-at91/board-dt.c
index 41d84d9..bb6b434 100644
--- a/arch/arm/mach-at91/board-dt.c
+++ b/arch/arm/mach-at91/board-dt.c
@@ -50,6 +50,7 @@
 static struct atmel_nand_data __initdata ek_nand_data = {
 	.ale		= 21,
 	.cle		= 22,
+	.det_pin	= -EINVAL,
 	.rdy_pin	= AT91_PIN_PC8,
 	.enable_pin	= AT91_PIN_PC14,
 };