RDMA/ocrdma: Obtain SL from device structure

Currently, driver obtains service level value from ah_attr->sl field.
However, this field is set to zero all the times from rdma-cm.  This
patch allows create_ah to obtain service level from dev->sl.

Signed-off-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>