image: Allow @ in node names when not using signatures

If signature verification is not in use we don't need to worry about
the risk of using @ in node names. Update fit_image_verify() to allow
it if the function is not enabled.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/image-fit.c

@@ -1377,7 +1377,7 @@ int fit_image_verify(const void *fit, int image_noffset)
 	size_t		size;
 	char		*err_msg = "";
 
-	if (strchr(name, '@')) {
+	if (IS_ENABLED(CONFIG_FIT_SIGNATURE) && strchr(name, '@')) {
 		/*
 		 * We don't support this since libfdt considers names with the
 		 * name root but different @ suffix to be equal