bnxt_en: Fix VF resource checking.

In bnxt_sriov_enable(), we calculate to see if we have enough hardware
resources to enable the requested number of VFs.  The logic to check
for minimum completion rings and statistics contexts is missing.  Add
the required checks so that VF configuration won't fail.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>