r8152: remove cancel_delayed_work_sync in rtl8152_set_speed

There is no conflict between the work_queue function and
rtl8152_set_speed(), so we don't have to cancel the delayed work in
rtl8152_set_speed().

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>