radeonsi: fix query buffer allocation

Fix the logic for buffer full check on alloc.

This patch just takes the fix Nicolai attached to the bug report
and updates it to work on master.

Fixes: e0f0d367 ("radeonsi: factor si_query_buffer logic out of si_query_hw")

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109561
(cherry picked from commit 603206d0)