for some reason the following commit was incorrect
769064de4b
Only the Sandstorm and Fury class should write this register.
Change-Id: Ie18f1da6e9b59fb99cca47aa93c7f2fee447ccea
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/400
Tested-by: jenkins