bnx2x: Prevent pci_disable_sriov with assigned VFs

Trying to disable sriov when VFs are assigned may lead to all kinds of problems.
This patch unifies the call in the driver to pci_disable_sriov() and prevents
them if some of the PF's child VFs are marked as assigned.

[Notice this is a bad scenario either way; User should not reach a point where
the OS tries to disable SRIOV when a VF is assigned - but currently there's no
way of preventing the user from doing so, and the ill-effect for the driver is
smaller this way]

Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: Ariel Elior <Ariel.Elior@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>