netfilter: xt_time: fix time's time_mt()'s use of do_div()

Fix netfilter xt_time's time_mt()'s use of do_div() on an s64 by using
div_s64() instead.

This was introduced by patch ee4411a1
("[NETFILTER]: x_tables: add xt_time match").

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>