weston-init: Make weston user member of seat group

This enables weston launch to access the seatd socket
/run/seatd.sock to communicate properly to acquire seat

(From OE-Core rev: c9f2ec1cccbf4b716364efd34a27138b34424212)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-graphics/wayland/weston-init.bb

@@ -102,6 +102,5 @@ FILES:${PN} += "\
 CONFFILES:${PN} += "${sysconfdir}/xdg/weston/weston.ini ${sysconfdir}/default/weston"
 
 SYSTEMD_SERVICE:${PN} = "weston.service weston.socket"
-USERADD_PARAM:${PN} = "--home /home/weston --shell /bin/sh --user-group -G video,input,render,wayland weston"
-GROUPADD_PARAM:${PN} = "-r wayland; -r render"
-
+USERADD_PARAM:${PN} = "--home /home/weston --shell /bin/sh --user-group -G video,input,render,seat,wayland weston"
+GROUPADD_PARAM:${PN} = "-r wayland; -r render; -r seat"