ivi-shell: Set view mask solely based on source rectangle

The controller sets the source and destination rectangles for any surface,
based on these parameters configure event is sent from the client application.

The controller commit the properties in the initial time, so
the view mask is capped to the current buffer dimensions of the
client. In runtime the client maybe sends some the bigger
configures of buffers. In this case view mask will be of smaller
dimension compared to the client buffer and it results in un-desired
clipping of client buffer.

To resolve this, use source rectangle as view mask. weston will take
care to clip the boundingbox of view to client buffer dimension if the
view mask is smaller.

Signed-off-by: Harsha M M <harsha.manjulamallikarjun@in.bosch.com>