[NETFILTER]: xt_tcpudp: fix wrong struct in udp_checkentry

It doesn't seem to have any effect on the x86 architecture but it does
have effect on the Axis CRIS architecture.

Signed-off-by: Jesper Bengtsson <jesper.bengtsson@axis.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>