MAINTAINERS: fix sorting

Take alphabetical orders for MAINTAINERS file.

Signed-off-by: Harry Wei <harryxiyou@gmail.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>