hdb: read_master_key add parens around (*mkey)

Add parens around the use of (*mkey)->next.

Change-Id: I3b60c2432d1c5dee8483795bed52ff24c7aa6a70

lib/hdb/mkey.c

@@ -149,7 +149,7 @@ read_master_keytab(krb5_context context, const char *filename,
     if (ret) {
 	/* do not return allocated memory on failure */
 	do {
-	    p = *mkey->next;
+	    p = (*mkey)->next;
 	    free(*mkey);
 	    *mkey = p;
 	} while (p != NULL);