power: supply: ab8500_charger: Fix an error handling path

power: supply: ab8500_charger: Fix an error handling path

'ret' is know to be 0 at this point, because it has not been updated by the
the previous call to 'abx500_mask_and_set_register_interruptible()'.

Fix it by updating 'ret' before checking if an error occurred.

Fixes: 84edbeeab67c ("ab8500-charger: AB8500 charger driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>