netfilter: nf_tables: typo NULL check in _clone() function

netfilter: nf_tables: typo NULL check in _clone() function

This should check for NULL in case memory allocation fails.

Reported-by: Julian Wiedmann <jwiedmann.dev@gmail.com>
Fixes: 062d62c00def ("netfilter: nft_limit: move stateful fields out of expression data")
Fixes: 5d08235807d6 ("netfilter: nft_connlimit: move stateful fields out of expression data")
Fixes: 23b3caeced8a ("netfilter: nft_last: move stateful fields out of expression data")
Fixes: 7822ec3a1976 ("netfilter: nft_quota: move stateful fields out of expression data")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Link: https://lore.kernel.org/r/20220110194817.53481-1-pablo@netfilter.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>