tracing: Use trace_iterator_reset() in tracing_read_pipe()

Currently tracing_read_pipe() open codes trace_iterator_reset(). Just have
it use trace_iterator_reset() instead.

Link: https://lkml.kernel.org/r/20211210202616.64d432d2@gandalf.local.home



Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>