netfilter: fix ptr_ret.cocci warnings

net/netfilter/nft_numgen.c:117:1-3: WARNING: PTR_ERR_OR_ZERO can be used
net/netfilter/nft_hash.c:180:1-3: WARNING: PTR_ERR_OR_ZERO can be used
net/netfilter/nft_hash.c:223:1-3: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Fixes: b9ccc07e ("netfilter: nft_hash: add map lookups for hashing operations")
Fixes: d734a288

 ("netfilter: nft_numgen: add map lookups for numgen statements")
CC: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: kbuild test robot <fengguang.wu@intel.com>
Acked-by: Laura Garcia Liebana <nevola@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>