Linux: Fix get_kernel_driver_active() when another app has claimed the interface

When another app has claimed the interface, IOCTL_USBFS_GETDRIVER will
succeed and report a driver of "usbfs" being attached.

Since this is not a regular kernel-driver (and detach_kernel_driver does
not detach it), get_kernel_driver_active() should return 0 in this case.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>