qed: return status of qed_iov_get_link

Clang static analysis reports this issue
qed_sriov.c:4727:19: warning: Assigned value is
  garbage or undefined
  ivi->max_tx_rate = tx_rate ? tx_rate : link.speed;
                   ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

link is only sometimes set by the call to qed_iov_get_link()
qed_iov_get_link fails without setting link or returning
status.  So change the decl to return status.

Fixes: 73390ac9 ("qed*: support ndo_get_vf_config")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>