qed/qed_sriov: guard against NULL derefs from qed_iov_get_vf_info

We have to make sure that the info returned by the helper is valid
before using it.

Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.

Fixes: f990c82c ("qed*: Add support for ndo_set_vf_trust")
Fixes: 733def6a ("qed*: IOV link control")
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>