opendous: Inhibit unnecessary state transitions

When current tap state and end state are the same, transitions are added which is not what should happen.
The usbprog driver was already patched like this long time ago.

Change-Id: I339e87156bdc7b5c83c10c14025b749605d3871a
Signed-off-by: Roman Reichel <romanreichel@aol.de>
Reviewed-on: http://openocd.zylin.com/1113
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>