MAINTAINERS: add Masami as a reviewer of hung task detector

Since I'm actively working on hung task blocker detector, add myself to a
reviewer of the HUNG TASK DETECTOR feature.

Link: https://lkml.kernel.org/r/175388550841.627474.3260499035226455392.stgit@devnote2


Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>