clk: renesas: r8a779a0: Remove non-existent S2 clock

The S2 internal core clock does not exist on R-Car V3U. Remove it.

Fixes: 17bcc803 ("clk: renesas: cpg-mssr: Add support for R-Car V3U")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20201019120614.22149-2-geert+renesas@glider.be