netconsole: remove a redundant netconsole_target_put()

This netconsole_target_put() is obviously redundant, and it
causes a kernel segfault when removing a bridge device which has
netconsole running on it.

This is caused by:

	commit 8d8fc29d
	Author: Amerigo Wang <amwang@redhat.com>
	Date:   Thu May 19 21:39:10 2011 +0000

	    netpoll: disable netpoll when enslave a device

Cc: David Miller <davem@davemloft.net>
 (for all 3.x stable releases)
Cc: stable@vger.kernel.org
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>