libarchive: correct upstream version check

libarchive: correct upstream version check

The directory index is missing the latest release:
https://www.libarchive.org/downloads/

Ticket (which I do not believe will be quickly fixed, considering
other similar open tickets):
https://github.com/libarchive/libarchive/issues/2693

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>