xserver-xorg: upgrade 21.1.4 -> 21.1.6

Changelog:

https://fossies.org/linux/misc/xorg-server-21.1.6.tar.xz/xorg-server-21.1.6/ChangeLog



Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 009e8d6a)
Signed-off-by: Steve Sakoman <steve@sakoman.com>