e1000e: potentially incorrect return for e1000_cfg_kmrn_10_100_80003es2lan

In the unlikely event that e1e_wphy() returns an error, the returned error
code value is not propogated to the caller of
e1000_cfg_kmrn_10_100_80003es2lan().

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>