AT91: Correct configuration define value

The MTD nand driver for Atmel chips is atmel_nand and not at91_nand anymore.
Change wrong configuration variables that were remaining.
Reported-by: Christoph Egger <siccegge@cs.fau.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/mach-at91/board-at572d940hf_ek.c

@@ -216,7 +216,7 @@ static struct atmel_nand_data __initdata eb_nand_data = {
 /*	.rdy_pin	= AT91_PIN_PC16, */
 	.enable_pin	= AT91_PIN_PA15,
 	.partition_info	= nand_partitions,
-#if defined(CONFIG_MTD_NAND_AT91_BUSWIDTH_16)
+#if defined(CONFIG_MTD_NAND_ATMEL_BUSWIDTH_16)
 	.bus_width_16	= 1,
 #else
 	.bus_width_16	= 0,

arch/arm/mach-at91/board-sam9m10g45ek.c

@@ -135,7 +135,7 @@ static struct atmel_nand_data __initdata ek_nand_data = {
 	.rdy_pin	= AT91_PIN_PC8,
 	.enable_pin	= AT91_PIN_PC14,
 	.partition_info	= nand_partitions,
-#if defined(CONFIG_MTD_NAND_AT91_BUSWIDTH_16)
+#if defined(CONFIG_MTD_NAND_ATMEL_BUSWIDTH_16)
 	.bus_width_16	= 1,
 #else
 	.bus_width_16	= 0,