netfilter: nf_tables: Sort labels in nft_netdev_hook_alloc()

No point in having err_hook_alloc, just call return directly. Also
rename err_hook_dev - it's not about the hook's device but freeing the
hook itself.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>