netfilter: nft_immediate: drop chain reference counter on error

In the init path, nft_data_init() bumps the chain reference counter,
decrement it on error by following the error path which calls
nft_data_release() to restore it.

Fixes: 4bedf9ee

 ("netfilter: nf_tables: fix chain binding transaction logic")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>