udp: fix if statement in SIOCINQ ioctl

We deleted a line of code and accidentally made the "return put_user()"
part of the if statement when it's supposed to be unconditional.

Fixes: 9f9a45be ('udp: do not expect udp headers on ioctl SIOCINQ')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>