power: supply: axp20x_usb_power: Add missing check in axp20x_usb_power_probe

There are two regmap_update_bits() calls but only one of them has
return value check, which is odd. Add a return value check and
terminate the execution flow on failure just like the other call.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>