drm/mgag200: Set cursor scanout address to correct BO

The hardware requires the correct memory address of the buffer. Currently
the same BO's address is programmed unconditionally, so only every second
cursor update actually becomes visible.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Fixes: 94dc57b1 ("drm/mgag200: Rewrite cursor handling")
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190723075425.24028-3-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_cursor.c

@@ -112,7 +112,7 @@ int mga_crtc_cursor_set(struct drm_crtc *crtc,
 			"failed to kmap cursor updates: %d\n", ret);
 		goto err_drm_gem_vram_unpin_dst;
 	}
-	gpu_addr = drm_gem_vram_offset(pixels_2);
+	gpu_addr = drm_gem_vram_offset(pixels_next);
 	if (gpu_addr < 0) {
 		ret = (int)gpu_addr;
 		dev_err(&dev->pdev->dev,