e1000: check return value of _get_speed_and_duplex

We were not checking the return value of get_speed_and_duplex
properly, whih may contain an error value.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>

1 file changed