ixgbe: Cleanup probe to remove redundant attempt to ID PHY

We always identify the PHY in our reset_hw path anyway so there is
no need to do it in get_invariants().  The reason I even noticed this
is that for new hardware (X550em) we don't assign some methods until
later in probe and calling phy.ops.read_reg could lead to a panic.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>