ixgbe: cleanup ixgbe_enumerate_functions

This function previously had the same check as used by the
ixgbe_pcie_from_parent. As the hardcode is due to the device having an internal
switch, this function should simply use the call from ixgbe_pcie_from_parent.
This reduces code complexity and makes it less likely a developer will forget
to update the list in the future.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>