netfilter: nf_tables: fix type mismatch with error return from nft_parse_u32_check

Commit 36b701fa ("netfilter: nf_tables: validate maximum value of
u32 netlink attributes") introduced nft_parse_u32_check with a return
value of "unsigned int", yet on error it returns "-ERANGE".

This patch corrects the mismatch by changing the return value to "int",
which happens to match the actual users of nft_parse_u32_check already.

Found by Coverity, CID 1373930.

Note that commit 21a9e0f1 ("netfilter: nft_exthdr: fix error
handling in nft_exthdr_init()) attempted to address the issue, but
did not address the return type of nft_parse_u32_check.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Cc: Laura Garcia Liebana <nevola@gmail.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 36b701fa ("netfilter: nf_tables: validate maximum value...")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>