sgi-xpc: update SGI XP/XPC/XPNET maintainer

Dean has moved on to other work.  His responsibilities for XP/XPC/XPNET
have been handed to me.

Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>