r600g/compute: Fix possible endless loop in compute_memory_pool allocations.

r600g/compute: Fix possible endless loop in compute_memory_pool allocations.

The important part is the change of the condition to <= 0. Otherwise the loop
gets stuck never actually growing the pool.

The change in the aux-need calculation guarantees max 2 iterations, and
avoids wasting memory in case a smaller item can't fit into a relatively larger
pool.

Reviewed-by: Bruno Jiménez <brunojimen@gmail.com>
Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>