[settings] Eliminate variable-length stack allocation

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/settings.c

 static struct settings *
 parse_settings_name ( const char *name, get_child_settings_t get_child ) {
 	struct settings *settings = &settings_root;
-	char name_copy[ strlen ( name ) + 1 ];
+	char *name_copy;
 	char *subname;
 	char *remainder;
 
 	/* Create modifiable copy of name */
-	memcpy ( name_copy, name, sizeof ( name_copy ) );
+	name_copy = strdup ( name );
+	if ( ! name_copy )
+		return NULL;
 	remainder = name_copy;
 
 	/* Parse each name component in turn */
 			break;
 	}
 
+	/* Free modifiable copy of name */
+	free ( name_copy );
+
 	return settings;
 }