usb: dwc3: isoc clean DWC3_EP_PENDING_REQUEST flag

After we kick_transfer we should clean
DWC3_EP_PENDING_REQUEST endpoint flag.

Signed-off-by: Janusz Dziedzic <januszx.dziedzic@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>