netfilter: nf_tables: Drop pointless memset in nf_tables_dump_obj

[ Upstream commit ff16111c ]

The code does not make use of cb->args fields past the first one, no
need to zero them.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Stable-dep-of: bd662c42 ("netfilter: nf_tables: Add locking for NFT_MSG_GETOBJ_RESET requests")
Signed-off-by: Sasha Levin <sashal@kernel.org>