dt-bindings: clock: renesas: cpg-mssr: Fix r8a774b1 typo

This patch fixes the typo %s/r8a774a1/r8a774b1/.

Fixes: 10003938 ("dt-bindings: clock: renesas: cpg-mssr: Document r8a774b1 binding")
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1576673984-37752-1-git-send-email-biju.das@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>