clk: sophgo: Fix return values of register updating helpers

clk: sophgo: Fix return values of register updating helpers

These helpers wrongly return the updated register value. As a non-zero
value indicates failure, this causes various clock operations are
considered failed.

Correct the return value to constant zero, since these simple MMIO
operations won't fail. This fixes clock enabling failures during booting
process,

	In:    serial@4140000
	Out:   serial@4140000
	Err:   serial@4140000
	Net:   Enable clock-controller@3002000 failed
	failed to enable clock 0
	No ethernet found.

which leads to misoperation of various peripherals.

Fixes: 5f364e072e7 ("clk: sophgo: cv1800b: Add clock controller driver for cv1800b SoC")
Tested-by: Yuguo Pei <purofle@gmail.com>
Signed-off-by: Yao Zi <ziyao@disroot.org>