power: supply: cros_charge-control: Fix signedness bug in charge_behaviour_store()

The C standard is vague about the signedness of enums, but in this case
here, they are treated as unsigned so the error handling does not work.
Use an int type to fix this.

Fixes: c6ed48ef ("power: supply: add ChromeOS EC based charge control driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/ZoWKEs4mCqeLyTOB@stanley.mountainSigned-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

drivers/power/supply/cros_charge-control.c

@@ -204,14 +204,13 @@ static ssize_t charge_behaviour_store(struct device *dev, struct device_attribut
 {
 	struct cros_chctl_priv *priv = cros_chctl_attr_to_priv(&attr->attr,
 							       CROS_CHCTL_ATTR_CHARGE_BEHAVIOUR);
-	enum power_supply_charge_behaviour behaviour;
 	int ret;
 
-	behaviour = power_supply_charge_behaviour_parse(EC_CHARGE_CONTROL_BEHAVIOURS, buf);
-	if (behaviour < 0)
-		return behaviour;
+	ret = power_supply_charge_behaviour_parse(EC_CHARGE_CONTROL_BEHAVIOURS, buf);
+	if (ret < 0)
+		return ret;
 
-	priv->current_behaviour = behaviour;
+	priv->current_behaviour = ret;
 
 	ret = cros_chctl_configure_ec(priv);
 	if (ret < 0)