power: supply: cpcap-battery: Fix coulomb counter calibration register use

The coulomb counter calibration is not CCO, it's CCM. And the CCM is
nine bits wide signed register, so let's use sign_extend32() for it.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>