vt: fix broken display when running aptitude

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>

drivers/tty/vt/vt.c

@@ -1551,7 +1551,7 @@ static void csi_K(struct vc_data *vc, int vpar)
 	scr_memsetw(start + offset, vc->vc_video_erase_char, 2 * count);
 	vc->vc_need_wrap = 0;
 	if (con_should_update(vc))
-		do_update_region(vc, (unsigned long) start, count);
+		do_update_region(vc, (unsigned long)(start + offset), count);
 }
 
 static void csi_X(struct vc_data *vc, int vpar) /* erase the following vpar positions */