power: supply: max14577: remove unneeded variable initialization

The local 'current_bits' variable does not have to be initialized
because all cases in following switch() either return or initialize it.

Addresses-Coverity: Unused value
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>