The previous patch for Tavor broke MemFree logic.

The driver should perform limit check only for Tavor.  For MemFree,
the check is incorrect, since ds (WQE stride) is always a power-of-2
(although the max_desc_size may not be).

In Tavor, however, WQE stride and desc_size are the same, and are not
necessarily power-of-2.  The check was really for the WQE stride (and
it Tavor, we use max_desc_size for the stride).
Signed-off-by: Jack Morgenstein <jackm@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>