power: supply: sc27xx: Introduce local variable 'struct device *dev'

Introduce local variable 'struct device *dev' and use it instead of
dereferencing it repeatly.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Reviewed-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>