stop dirty logging while updating cirrus bank memory (Glauber Costa)

Otherwise, slot tracking gets confused.

This fixes a screen corruption bug with Ubuntu guest installation.

Signed-off-by: Glauber Costa <glommer@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6851 c046a42c-6fe2-441c-8c8c-71466251a162
