tools: Pass the key blob around

At present we rely on the key blob being in the global_data fdt_blob
pointer. This is true in U-Boot but not with tools. For clarity, pass the
parameter around.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_fit.c b/common/spl/spl_fit.c
index 774072b..1bbf824 100644
--- a/common/spl/spl_fit.c
+++ b/common/spl/spl_fit.c
@@ -321,7 +321,8 @@
 	if (CONFIG_IS_ENABLED(FIT_SIGNATURE)) {
 		printf("## Checking hash(es) for Image %s ... ",
 		       fit_get_name(fit, node, NULL));
-		if (!fit_image_verify_with_data(fit, node, src, length))
+		if (!fit_image_verify_with_data(fit, node, gd_fdt_blob(), src,
+						length))
 			return -EPERM;
 		puts("OK\n");
 	}