tracing: Update MAINTAINERS file to include tracepoint.c

Updates to the tracepoint.c file should not only be Cc'd to LKML, but also
to linux-trace-kernel@vger.kernel.org. But because it is not listed in the
MAINTAINERS file, it does not get added.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250304103724.174ecb36@gandalf.local.home


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