IB/mlx4: Fix incorrect order of formal and actual parameters

The last two actual parameters when calling id_map_find_by_sl_id()
from id_map_get() are swapped. However, the same formal parameters to
id_map_get() have them swapped as well, inverting the effect of the
first error.

This commit improves readability, but makes no functional change to
the code.

Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Wengang Wang <wen.gang.wang@oracle.com>
Reviewed-by: Knut Omang <knut.omang@oracle.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>