tracing: Use memset_startat helper in trace_iterator_reset()

Make use of memset_startat helper to simplify the code, there should be
no functional change as a result of this patch.

Link: https://lkml.kernel.org/r/20211210012245.207489-1-xiujianfeng@huawei.comSigned-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.h

@@ -1932,14 +1932,7 @@ extern struct trace_iterator *tracepoint_print_iter;
  */
 static __always_inline void trace_iterator_reset(struct trace_iterator *iter)
 {
-	const size_t offset = offsetof(struct trace_iterator, seq);
-
-	/*
-	 * Keep gcc from complaining about overwriting more than just one
-	 * member in the structure.
-	 */
-	memset((char *)iter + offset, 0, sizeof(struct trace_iterator) - offset);
-
+	memset_startat(iter, 0, seq);
 	iter->pos = -1;
 }