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 <[e-mail]>
Cc: Joe Perches <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

.get_maintainer.ignore

···
+Christoph Hellwig <[e-mail]>