ui/gtk-egl: fix scaling for cursor position in scanout mode

vc->gfx.w and vc->gfx.h are not updated appropriately in this code path,
which leads to a different scaling factor for rendering the cursor on
some edge cases (e.g. the focus has left and re-entered the gtk window).
This can be reproduced using vhost-user-gpu with the gtk ui on the x11
backend.
Use the surface dimensions which are already updated accordingly.

Signed-off-by: Erico Nunes <ernunes@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230320160856.364319-2-ernunes@redhat.com>
(cherry picked from commit f8a951b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

ui/gtk-egl.c

@@ -88,8 +88,8 @@ void gd_egl_draw(VirtualConsole *vc)
 #endif
         gd_egl_scanout_flush(&vc->gfx.dcl, 0, 0, vc->gfx.w, vc->gfx.h);
 
-        vc->gfx.scale_x = (double)ww / vc->gfx.w;
-        vc->gfx.scale_y = (double)wh / vc->gfx.h;
+        vc->gfx.scale_x = (double)ww / surface_width(vc->gfx.ds);
+        vc->gfx.scale_y = (double)wh / surface_height(vc->gfx.ds);
 
         glFlush();
 #ifdef CONFIG_GBM