smb138x: fix WD bite

Commit 85635da4 ("qcom-charger: smb138x: fix buck damage on
v1.1 hardware") introduced wa_flags as the first member
in the struct. However there are implict assumptions in the driver that
the first member is the library structure. This causes memory corruption
and an eventual watch dog bite reset.

Fix it by ensuring that the library struct is explicitly initialized
from the parent struct.

CRs-Fixed: 1055113
Change-Id: I38474a228ec7b245dc330b4a37847c9f1bf29c2a
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>