hw/qxl: qxl_dirty_surfaces: use uintptr_t

As suggested by Paolo Bonzini, to avoid possible integer overflow issues.
Signed-off-by: NAlon Levy <alevy@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/qxl.c

@@ -1804,7 +1804,7 @@ static void qxl_hw_text_update(void *opaque, console_ch_t *chardata)
 
 static void qxl_dirty_surfaces(PCIQXLDevice *qxl)
 {
-    intptr_t vram_start;
+    uintptr_t vram_start;
     int i;
 
     if (qxl->mode != QXL_MODE_NATIVE && qxl->mode != QXL_MODE_COMPAT) {
@@ -1815,7 +1815,7 @@ static void qxl_dirty_surfaces(PCIQXLDevice *qxl)
     qxl_set_dirty(&qxl->vga.vram, qxl->shadow_rom.draw_area_offset,
                   qxl->shadow_rom.surface0_area_size);
 
-    vram_start =  (intptr_t)memory_region_get_ram_ptr(&qxl->vram_bar);
+    vram_start = (uintptr_t)memory_region_get_ram_ptr(&qxl->vram_bar);
 
     /* dirty the off-screen surfaces */
     for (i = 0; i < qxl->ssd.num_surfaces; i++) {