vt: fix broken display when running aptitude

commit 943210ba807ec50aafa2fa7b13bd6d36a478969b upstream.

If you run aptitude on framebuffer console, the display is corrupted. The
corruption is caused by the commit d8ae7242. The patch adds "offset" to
"start" when calling scr_memsetw, but it forgets to do the same addition
on a subsequent call to do_update_region.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: d8ae7242 ("vt: preserve unicode values corresponding to screen characters")
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Cc: stable@vger.kernel.org	# 4.19
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>