extcon: axp288: Handle reserved charger-type values better

According to the data sheets all the values not handled in the
switch-case are "reserved". Update the dev_warn message to reflect
this and set the cable-type to EXTCON_CHG_USB_SDP (so max 500mA
current draw) as safe default.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>