PVS-Studio warning V547 for libusb

int linux_get_device_address (....,
  uint8_t *busnum, uint8_t *devaddr,
  ....)
{
  ....
  *busnum = __read_sysfs_attr(ctx, sys_name, "busnum");
  if (0 > *busnum)
    return *busnum;

  *devaddr = __read_sysfs_attr(ctx, sys_name, "devnum");
  if (0 > *devaddr)
    return *devaddr;
  ....
}

This suspicious code was found in libusb project by PVS-Studio static code analyzer.
Warning message is:
V547 Expression '0 > * busnum' is always false. Unsigned type value is never < 0. linux_usbfs.c 620

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/