clk: renesas: cpg-mssr: Update kerneldoc for struct cpg_mssr_priv

New fields were added, but kerneldoc was forgotten, or inserted at the
wrong place.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>