power: supply: sc27xx: Fix capacity saving function

We found sometimes we can not get the saving capacity to initialize the
battery capacity, the reason is the user area registers are put on power
always-on region, so we need delay some time to wait until values are
updated successfully.

Moreover we also should clear the USER_AREA_CLEAR register after setting
the USER_AREA_SET register, otherwise we can not save the values in the
USER_AREA_SET register.

Signed-off-by: Yuanjiang Yu <yuanjiang.yu@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>