e1000e: Fix check_for_link return value with autoneg off

When autoneg is off, the .check_for_link callback functions clear the
get_link_status flag and systematically return a "pseudo-error". This means
that the link is not detected as up until the next execution of the
e1000_watchdog_task() 2 seconds later.

Fixes: 19110cfb ("e1000e: Separate signaling for link check/link up")
Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Acked-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>