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: 3b9e2ea6c11b ("netfilter: nft_limit: move stateful fields out of expression data")
Fixes: 37f319f37d90 ("netfilter: nft_connlimit: move stateful fields out of expression data")
Fixes: 33a24de37e81 ("netfilter: nft_last: move stateful fields out of expression data")
Fixes: ed0a0c60f0e5 ("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>