MAINTAINERS: add missing : after HR Timers F tag

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