qxl: always update displaysurface on resize

qxl: always update displaysurface on resize

Don't try to be clever and skip displaysurface reinitialization in case
the size hasn't changed.  Other parameters might have changed
nevertheless, for example depth or stride, resulting in rendering being
broken then.

Trigger: boot linux guest with vesafb, start X11, make sure both vesafb
and X11 use the display same resolution.  Then watch X11 screen being
upside down.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 0ec8df3974d2a4ff95b5fd4785b9bd3def7252f3)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>