bblayers.conf: move meta-oniro-staging layer order

Layers order decides on the override of classes (layer priorities do
not work for this [1]). To override a class from poky we need to
move the overriding class (which is in meta-oniro-staging) before on
the layers list.

[1] https://www.yoctoproject.org/pipermail/yocto/2012-January/004379.html



Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>