read_word
cap_reg = read_word(fd, bus, dev, func, cap_ptr, &ret);
link_status = read_word(fd, bus, dev, func,
sec_status = read_word(fd, bus, dev, func,
cap_reg = read_word(fd, bus, dev, func, cap_ptr, &ret);
static uint16_t read_word(int fd, int bus, int dev, int func, int offset,