power: fg/smbcharger: fix usage of un-initialized variable

Initialize variables to valid values before using them in
charger and FG drivers.

CRs-Fixed: 996609
Change-Id: Iacf7af719374c90d01f3e961f4fe1728a32314a3
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>