arm64: dts: renesas: r8a77995: Use r8a7795-cpg-mssr binding definitions

Replace the hardcoded clock indices by R8A77995_CLK_* symbols.

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