IB/mlx4: Optimize freeing of items on error unwind

On failure, we loop through all possible pointers and test them before
calling kfree.  But really, why even attempt to free items we didn't
allocate when we can easily loop through exactly and only the devices
for which the original memory allocation succeeded and free just those.

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>