igb: Fix potential memory leak in igb_add_ethtool_nfc_entry

Add check for return of igb_update_ethtool_nfc_entry so that in case
of any potential errors the memory alocated for input will be freed.

Fixes: 0e71def2

 ("igb: add support of RX network flow classification")
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: Mateusz Palczewski <mateusz.palczewski@intel.com>
Tested-by: Arpana Arland <arpanax.arland@intel.com> (A Contingent worker at Intel)
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>