team: lb: use sizeof(*fprog) in __fprog_create

sock_fprog and sock_fprog_kern are of equal size, however
it's cleaner to just use sizeof(*fprog) instead to always
have correct type.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>