ixgbe: fix incorrect status check

Check for ret_val instead of !ret_val to allow the rest of
the code to execute and configure the speed properly.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>