Simplify sriov enable/disable flow for below two checks.
1. PCI core driver allows sriov configuration only on a PF.
This is done in drivers/pci/pci-sysfs.c sriov_attrs_are_visible().
2. PCI core driver allow sriov enablement if the sriov is currently
disabled for for a PF. This is done in drivers/pci/pci-sysfs.c
sriov_numvfs_store().
Hence there is no need for mlx5 driver to duplicate such checks.