clk: renesas: div6: Always use readl()/writel()

clk: renesas: div6: Always use readl()/writel()

On arm32/arm64, there is no reason to use the (soon deprecated)
clk_readl()/clk_writel().  Hence use the generic readl()/writel()
instead.

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