clk: renesas: r8a77965: Replace DU2 clock

R-Car M3-N does not have the DU2 unit but it has DU3 instead.
Fix the module clock definition to reflect that.

Fixes: 7ce36da9 ("clk: renesas: cpg-mssr: Add support for R-Car M3-N")
Reported-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>