fix the issue of pivot_root on busybox
fix the issue of pivot_root on busybox

Busybox's pivot_root is not the same with linux-utils's
pivot_root, fix this issue in this patch.

Signed-off-by: Fupan Li <30fd179d1a704171deeab5eaee24dcfab6c509a1@windriver.com>

fluxos-iot/meta-flux,fluxos-iot/meta-flux,fluxos-iot/meta-flux