rockchip: clk: rk3399: 24MHz is not a power of 2

The clock driver for the RK3399 mistakenly used (24 * 2^20) where it
should have used (24 * 10^6) in a few calculations.

This commits fixes this.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>