mfd: sc27xx: Use SoC compatible string for PMIC devices

We should use SoC compatible string in stead of wildcard string for
PMIC child devices.

Fixes: 0419a75b (arm64: dts: sprd: Remove wildcard compatible string)
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>