spl: add check for FIT-header when loading image

Add check for FDT_MAGIC, otherwise also legacy images will be loaded as
a FIT. With this check in place, the loader works correct both
with legacy and FIT images.

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
Acked-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/spl/spl_spi.c

@@ -99,7 +99,8 @@ static int spl_spi_load_image(struct spl_image_info *spl_image,
 		if (err)
 			return err;
 
-		if (IS_ENABLED(CONFIG_SPL_LOAD_FIT)) {
+		if (IS_ENABLED(CONFIG_SPL_LOAD_FIT) &&
+			image_get_magic(header) == FDT_MAGIC) {
 			struct spl_load_info load;
 
 			debug("Found FIT\n");