clk: sunxi-ng: h6: fix bus clocks' divider position

The bus clocks (AHB/APB) on Allwinner H6 have their second divider start
at bit 8, according to the user manual and the BSP code. However,
currently the divider offset is incorrectly set to 16, thus the divider
is not correctly read and the clock frequency is not correctly calculated.

Fix this bit offset on all affected bus clocks in ccu-sun50i-h6.

Cc: stable@vger.kernel.org # v4.17.y
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>