net/mlx5: Simplify sriov enable/disable flow

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.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Bodong Wang <bodong@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>