r8152: don't execute runtime suspend if the tx is not empty

[ Upstream commit 6a0b76c0 ]

Runtime suspend shouldn't be executed if the tx queue is not empty,
because the device is not idle.

Signed-off-by: Hayes Wang <hayeswang@realtek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>