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

Issue discovered through static analysis.
Signed-off-by: NDave Ertman <david.m.ertman@intel.com>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>