MAINTAINERS: Add uprobes entry

Add uprobes entry to MAINTAINERS to clarify the maintainers.

Link: https://lore.kernel.org/all/172074397710.247544.17045299807723238107.stgit@devnote2/



Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>