present/wnmd: Translate update region to screen space

The region as passed in is in the source pixmap's coordinate space, so
intersecting it with the clipList (which is in screen space) resulted in
disappointment.

Fixes Firefox popups such as the hamburger menu when using the EGL
backend.

v2:
* Drop vblank->x/y_off from RegionTranslate call, since they're always
  0 here (present_wnmd_check_flip rejects flips for x/y_off != 0).

Reported-by: Robert Mader <robert.mader@posteo.de>
Tested-by: Robert Mader <robert.mader@posteo.de>
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
Tested-by: Joakim Tjernlund <joakim.tjernlund@infinera.com> # v1
4 jobs for present_wnmd_execute-update-coordinate-space in 7 minutes and 32 seconds (queued for 1 second)
Status Job ID Name Coverage
  Docker Image
passed #5883821
debian-buster

00:00:10

 
  Build And Test
passed #5883822
autotools

00:07:21

passed #5883823
meson

00:00:56

passed #5883824
meson-noglamor

00:00:54