usbnet: smsc95xx: fix suspend failure

The three below functions:

	smsc95xx_enter_suspend0()
	smsc95xx_enter_suspend1()
	smsc95xx_enter_suspend2()

return > 0 in case of success, so they will cause smsc95xx_suspend()
to return > 0 and cause suspend failure.

The bug is introduced in commit 3b9f7d(smsc95xx: fix error handling
in suspend failure case).

Cc: <stable@vger.kernel.org>		[3.8]
Cc: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>