pc-bios/s390-ccw/libc: size_t should be unsigned

qemu/pc-bios/s390-ccw/libc.c:82]: (style) Unsigned variable 'num_idx' can't be negative so it is unnecessary to test it.

Source code is


    while (num_idx >= 0) {

but

    size_t num_idx = 1; /* account for NUL */

So there is no escape from the while loop.