3c59x: Ensure to apply the expires time

In commit 5b6490de ("3c59x: Use setup_timer()") Amitoj
removed add_timer which sets up the epires timer.  In this patch
the behavior is restore but it uses mod_timer which is a bit more
compact.

Signed-off-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>