app/eventdev: remove unnecessary barrier from order test

app/eventdev: remove unnecessary barrier from order test

For "order_launch_lcores" function, wmb after that the main lcore
updates the variable "t->err", which represents the end of the test
signal, is unnecessary. Because after the main lcore updates this
signal variable, it will jump out of the launch function loop, and wait
other lcores stop or return error in the main function(evt_main.c).
During this time, there is no storing operation and thus no need for
wmb.

Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>