power: smb135x-charger: handle USB removal in over voltage properly

In current design, we notify the usb present status when charger voltage
comes back from an over voltage(OV) condition. There is another possibility
where the charger is removed from an OV state in which case the usb present
state should not be notified. Add logic to handle this.

CRs-Fixed: 880466
Change-Id: Ibfefda250ea7689080cb8b567747e2e51a2aa3f5
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>