ixgbe: fix potential null dereference

This patch adds a default case which goes to the next loop iteration
in the case where p is not set, preventing p from being dereferenced.

Signed-off-by: Josh Hay <joshua.a.hay@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c

@@ -1040,6 +1040,9 @@ static void ixgbe_get_ethtool_stats(struct net_device *netdev,
 			p = (char *) adapter +
 					ixgbe_gstrings_stats[i].stat_offset;
 			break;
+		default:
+			data[i] = 0;
+			continue;
 		}
 
 		data[i] = (ixgbe_gstrings_stats[i].sizeof_stat ==