qcom: smb2: fix probe failure

Charger driver probe might fail while querying for battery
health if bms psy is not available. Fix this by reporting
health as "UNKNOWN".

CRs-Fixed: 2029960
Change-Id: I6544788a6fe3ab7aaf70ffd382213d8b4aa4c0b6
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>