RDMA/mlx5: Fix assigning access flags to cache mkeys

RDMA/mlx5: Fix assigning access flags to cache mkeys

After the change to use dynamic cache structure, new cache entries
can be added and the mkey allocation can no longer assume that all
mkeys created for the cache have access_flags equal to zero.

Example of a flow that exposes the issue:
A user registers MR with RO on a HCA that cannot UMR RO and the mkey is
created outside of the cache. When the user deregisters the MR, a new
cache entry is created to store mkeys with RO.

Later, the user registers 2 MRs with RO. The first MR is reused from the
new cache entry. When we try to get the second mkey from the cache we see
the entry is empty so we go to the MR cache mkey allocation flow which
would have allocated a mkey with no access flags, resulting the user getting
a MR without RO.

Fixes: dd1b913fb0d0 ("RDMA/mlx5: Cache all user cacheable mkeys on dereg MR flow")
Reviewed-by: Edward Srouji <edwards@nvidia.com>
Signed-off-by: Michael Guralnik <michaelgur@nvidia.com>
Link: https://lore.kernel.org/r/8a802700b82def3ace3f77cd7a9ad9d734af87e7.1695203958.git.leonro@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>