examples/vhost: fix lcore initialization

examples/vhost: fix lcore initialization

when "TAILQ_INIT()" was added to the loop of "for (lcore_id = 0; ...)"
statement, the assignment to "lcore_ids" was removed out of the loop.
It changed the original initialization of "lcore_ids".

Fix it by introducing two braces.

Fixes: 45657a5c6861 ("examples/vhost: use tailq to link vhost devices")
Cc: stable@dpdk.org
Signed-off-by: Yong Wang <wang.yong19@zte.com.cn>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>