drivers: usb: common: nrf_usbd_common: Handle USB SoF IRQ first

The processing order is relevant if the IRQ handler call is delayed and
multiple interrupts are pending. Handle USB SoF before other interrupts
to ensure that it would be reported before other USB events (e.g. before
completed USB data transfers).

Signed-off-by: Marek Pieta <Marek.Pieta@nordicsemi.no>