Add hch to .get_maintainer.ignore

While the idea behind get_maintainer seems highly useful it's
unfortunately way to trigger happy to grab people that once had a few
commits to files.  For someone like me who does a lot of tree-wide API
work that leads to an incredible amount of Cc spam.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>