tools: iio: replace seekdir() in iio_generic_buffer

Replace seekdir() with rewinddir() in order to fix a localized glibc bug.

One of the glibc patches that stable Gentoo is using causes an improper
directory stream positioning bug on 32bit arm. That in turn ends up as a
floating point exception in iio_generic_buffer.

The attached patch provides a fix by using an equivalent function which
should not cause trouble for other distros and is easier to reason about
in general as it obviously always goes back to to the start.

https://sourceware.org/bugzilla/show_bug.cgi?id=31212

Signed-off-by: Petre Rodan <petre.rodan@subdimension.ro>
Link: https://lore.kernel.org/r/20240108103224.3986-1-petre.rodan@subdimension.ro
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>