board: atmel: use get_nand_dev_by_index()

As part of preparation for nand DM conversion the new API has been
introduced to remove direct access to nand_info array. So, use it here
instead of accessing to nand_info array directly.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
diff --git a/board/atmel/at91sam9x5ek/at91sam9x5ek.c b/board/atmel/at91sam9x5ek/at91sam9x5ek.c
index 1e4a4a2..2452e63 100644
--- a/board/atmel/at91sam9x5ek/at91sam9x5ek.c
+++ b/board/atmel/at91sam9x5ek/at91sam9x5ek.c
@@ -175,7 +175,7 @@
 			dram_size += gd->bd->bi_dram[i].size;
 		nand_size = 0;
 		for (i = 0; i < CONFIG_SYS_MAX_NAND_DEVICE; i++)
-			nand_size += nand_info[i]->size;
+			nand_size += get_nand_dev_by_index(i)->size;
 		lcd_printf("  %ld MB SDRAM, %ld MB NAND\n",
 			dram_size >> 20,
 			nand_size >> 20);