drivers: udc_dwc2: Mark endpoint idle on disable while hibernated

When endpoint is disabled while hibernated, the UDC endpoint state has
to be reset. Set the busy to false to keep UDC endpoint state in sync
with peripheral register state.

Fixes: 2be960ad ("drivers: udc_dwc2: Disable endpoint while
hibernated")

Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>