Fix misaligned buffer in env_fat_save

When saving the environment on a platform which has DMA alignment
larger than the natural alignment, env_fat_save triggers a debug
message in file_fat_write:

  Saving Environment to FAT... writing uboot.env
  FAT: Misaligned buffer address (9df1c8e0)
  OK

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>

env/fat.c

@@ -36,7 +36,7 @@ DECLARE_GLOBAL_DATA_PTR;
 #ifdef CMD_SAVEENV
 static int env_fat_save(void)
 {
-	env_t	env_new;
+	env_t __aligned(ARCH_DMA_MINALIGN) env_new;
 	struct blk_desc *dev_desc = NULL;
 	disk_partition_t info;
 	int dev, part;