boot: Use fit_image_get_data() to get data

Use this function instead of fit_image_get_emb_data() data, since it
works will FITs that use external data.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/lib/bootm.c b/arch/x86/lib/bootm.c
index 90c0376..b37f42f 100644
--- a/arch/x86/lib/bootm.c
+++ b/arch/x86/lib/bootm.c
@@ -104,9 +104,9 @@
 		is_zimage = 1;
 #if defined(CONFIG_FIT)
 	} else if (images->fit_uname_os && is_zimage) {
-		ret = fit_image_get_emb_data(images->fit_hdr_os,
-					     images->fit_noffset_os,
-					     (const void **)&data, &len);
+		ret = fit_image_get_data(images->fit_hdr_os,
+					 images->fit_noffset_os,
+					 (const void **)&data, &len);
 		if (ret) {
 			puts("Can't get image data/size!\n");
 			goto error;