ivi-shell: bugfix, add ref_count to ivi_layout_layer

ivi-shell: bugfix, add ref_count to ivi_layout_layer

if a controller calls ivi_layout_layer_create_with_demenstion with a ID
which is already created before, the API returns exist ivi_layer.
However addtionally, it shall count up ref count to destroy ivi_layer
when ref count is 0. The previous code will destroy ivi_layer
immediately even if the other code still refers ivi_layer.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>