anv: fix descriptor set free

anv: fix descriptor set free

Once we start going through the free list of the descriptor set pool,
we might use a free entry larger than the descriptor set we want to
allocate. When we free that descriptor set, we use the size of the set
rather than the size of the entry that was picked. This leads to leaks
of some amount of descriptor set pool.

This fix saves the size of the entry in the descriptor set so we know
what amount of the pool needs to freed.

v2: Don't bother adding a new size field

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Cc: <mesa-stable@lists.freedesktop.org>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3324
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6084>