MAINTAINERS: add LTP info to the list

Cc: Subrata Modak <subrata@linux.vnet.ibm.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>