r8152: return -EBUSY for runtime suspend

Remove calling cancel_delayed_work_sync() for runtime suspend,
because it would cause dead lock. Instead, return -EBUSY to
avoid the device enters suspending if the net is running and
the delayed work is pending or running. The delayed work would
try to wake up the device later, so the suspending is not
necessary.

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