power: supply: axp288_charger: Actually get and use the USB_HOST extcon device

Nothing was setting info->otg.cable, so the extcon_get_cable_state_
calls on it would always return -EINVAL.

This commit fixes this by actually setting info->otg.cable using the new
extcon_get_extcon_dev_by_cable_id function.

This commit also makes failing to register the extcon notifier for the
USB_HOST cable an error rather then a warning, because we MUST have this
notfier to properly disable the VBUS path when in host mode so that we're
not drawing current from the 5V boost converter which is supplying power
to the otg port when in host mode.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>