clk: renesas: cpg-mssr: Adjust r8a77980 ifdef

Adjust the R8A77980-specific #ifdefs to use CLK instead of ARCH
to follow same style as other SoCs.

Fixes: ce15783c ("clk: renesas: cpg-mssr: add R8A77980 support")
Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>