crypto: chtls - remove redundant null pointer check before kfree_skb

kfree_skb has taken the null pointer into account. hence it is safe
to remove the redundant null pointer check before kfree_skb.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>