add get charing current api for discrete_charger_class factory tcmd will use this api Change-Id: I1a6011fcf7b936329e6ae1b7787b6e86078b8915 Signed-off-by: liuyc20 <liuyc20@lenovo.com> Reviewed-on: https://gerrit.mot.com/2090448 SME-Granted: SME Approvals Granted SLTApproved: Slta Waiver Tested-by: Jira Key Reviewed-by: Haijian Ma <mahj8@motorola.com> Reviewed-by: Huosheng Liao <liaohs@motorola.com> Submit-Approved: Jira Key