USB: dwc3_otg: Cancel charger detection work before entering LPM

Charger detection algorithm takes significant time (hundreds of msec)
to complete. This can result in a scenario where chg_det work is
pending to run even after cable disconnection. Since, USB clocks are
turned off after cable disconnect, hence, execution of detection-work
later can result in unlocked register accesses. Hence, cancel any
pending charger detection work before turning off clocks.

CRs-Fixed: 422848
Change-Id: Iccaba4c003ee492b84bce057de64a2ae8edc2ef6
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>