ivi-layout: fix transform matrix could not be invertible in update_scale

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>
To get resolution of a screen, refer width and height of screen's of weston_output.

Priviously, this code refers width and height of current_mode. However it is not always available. E.g. on Tizen.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>