power: smb135x-charger: Fix battery missing status indication

The battery missing bit being set indicates that the battery is
missing, update the batt_present variable with correct status.

Change-Id: I58fb2d0ed78b3695723f6159ba06b15aa479b0ef
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>