netfilter: nf_tables: nft_parse_register can return a negative value

Since commit 6e1acfa3 ("netfilter: nf_tables: validate registers
coming from userspace.") nft_parse_register can return a negative value,
but the function prototype is still returning an unsigned int.

Fixes: 6e1acfa3 ("netfilter: nf_tables: validate registers coming from userspace.")
Signed-off-by: NAntoine Tenart <atenart@kernel.org>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -9363,7 +9363,7 @@ int nft_parse_u32_check(const struct nlattr *attr, int max, u32 *dest)
 }
 EXPORT_SYMBOL_GPL(nft_parse_u32_check);
 
-static unsigned int nft_parse_register(const struct nlattr *attr, u32 *preg)
+static int nft_parse_register(const struct nlattr *attr, u32 *preg)
 {
 	unsigned int reg;