ab8500-charger: AB workaround for invalid charger

AB8500 refuses to start charging when some types of non standard
chargers are connected. This change force the AB to start charging.

Signed-off-by: Henrik Sölver <henrik.solver@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Yvan FILLION <yvan.fillion@stericsson.com>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>
Tested-by: Yvan FILLION <yvan.fillion@stericsson.com>