ARM: shmobile: r8a7740: tidyup comment/implementation mismatch

Current clock-r8a7740's DIV4/DIV6/MSTP implemented area and
its comment are mismatching.
This patch tidyup its comment/implementation area.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>