IB/core: Don't warn on no SA support in event handler

Registering an event handler is done for a device. This device may have
one RoCE port (no SA cap) and one InfiniBand port (has SA cap).
Therefore, warning from the event handler about a specific port that
doesn't have SA cap is correct but pollutes the kernel log without a
need.

Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>