MAINTAINERS: correct 9P FILE SYSTEM git entry

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>