clk: renesas: Remove use of ARCH_R8A7796

CONFIG_ARCH_R8A7796 was renamed to CONFIG_ARCH_R8A77960 in commit
39e57e14 ("soc: renesas: Add ARCH_R8A77960 for existing R-Car
M3-W"), so its users can be removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20191211100220.6854-1-geert+renesas@glider.be