MAINTAINERS: Update the PTRACE entry

Document the status quo: Roland has been busy with other projects for years,
so list Oleg as the de-facto maintainer.

Also update the file patterns.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roland McGrath <roland@hack.frob.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>