netfilter: nft_redir: fix sparse warnings

>> net/netfilter/nft_redir.c:39:26: sparse: incorrect type in assignment (different base types)
   net/netfilter/nft_redir.c:39:26:    expected unsigned int [unsigned] [usertype] nla_be32
   net/netfilter/nft_redir.c:39:26:    got restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:40:40: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:46:34: sparse: incorrect type in assignment (different base types)
   net/netfilter/nft_redir.c:46:34:    expected unsigned int [unsigned] [usertype] nla_be32
   net/netfilter/nft_redir.c:46:34:    got restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32
>> net/netfilter/nft_redir.c:47:48: sparse: cast to restricted __be32

Fixes: e9105f1b

 ("netfilter: nf_tables: add new expression nft_redir")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>