e1000e: Add code to check return values on NVM accesses

Adding code to check and respond to previously ignored return values
from NVM access functions.

Issue discovered through static analysis.

Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>