usbip: vhci_hcd: fix calling usb_hcd_giveback_urb() with irqs enabled

usbip: vhci_hcd: fix calling usb_hcd_giveback_urb() with irqs enabled

kcov testing uncovered call to usb_hcd_giveback_urb() without disabling
interrupts.

Link: https://lore.kernel.org/linux-usb/CAAeHK+wb4k-LGTjK9F5YbJNviF_+yU+wE_=Vpo9Rn7KFN8vG6Q@mail.gmail.com/
usb_hcd_giveback_urb() is called from vhci's urb_enqueue, when it
determines it doesn't need to xmit the urb and can give it back.
This path runs in task context.

Disable irqs around usb_hcd_giveback_urb() call.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20201006223914.39257-1-skhan@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>