IB/mlx4: Do not attemp to report HCA clock offset on VFs

mlx4 VFs can provide CQE raw time-stamping services, but they
don't have the hca core clock mapped to their PCI bars.

As such, we should not attempt to query and report the clock offset
to user space for VFs. Doing so causes query_device over VFs to fail
with -ENOSUPP.

Fixes: 4b664c43 ('IB/mlx4: Add support for CQ time-stamping')
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>