clk: renesas: r8a77990: Fix incorrect PLL0 divider in comment

PLL0 runs at 4.8 GHz, i.e. EXTAL x 100.

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