ethtool: potential NULL dereference in strset_prepare_data()

Smatch complains that the NULL checking isn't done consistently:

    net/ethtool/strset.c:253 strset_prepare_data()
    error: we previously assumed 'dev' could be null (see line 233)

It looks like there is a missing return on this path.

Fixes: 71921690 ("ethtool: provide string sets with STRSET_GET request")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/strset.c

@@ -239,6 +239,7 @@ static int strset_prepare_data(const struct ethnl_req_info *req_base,
 				return -EINVAL;
 			}
 		}
+		return 0;
 	}
 
 	ret = ethnl_ops_begin(dev);