power: pm8921-charger: reset chg failed bit regularly

The charger was observed to freeze for unknown reasons. Clear the failed
bit upon insertion/removal of usb. Also clear that bit in eoc check worker
and the heartbeat worker.

Change-Id: I6419b7ecbfc4d9b73537285357be1e810efa0411
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>