anv/allocator: Compare to start_offset in state_pool_free_no_vg

anv/allocator: Compare to start_offset in state_pool_free_no_vg

In d11e4738a86ec, we started using a start_offset to allow us to
allocate pools where the base address isn't at the start of the pool.
This is useful for binding table pools which want to be relative to
surface state base address (more or less), among other things.  However,
we had a bug where, if you have a negative offset, everything returned
to the pool would end up being returned to the "back" of the pool.  This
isn't what we want for binding tables in the softpin world.  This was
causing us to never actually re-use any binding table blocks.  How this
passed CTS, I have no idea.

Closes: #3100
Fixes: d11e4738a86ec "anv/allocator: Add a start_offset to anv_state_pool"
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5395>