e1000e: potentially incorrect return for e1000e_setup_fiber_serdes_link

In the unlikely event that e1000_poll_fiber_serdes_link_generic() is called
and it returns an error, the returned error code value is not propagated to
the caller of e1000e_setup_fiber_serdes_link().

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>