shell: fix maximizing windows on a secondary output
shell: fix maximizing windows on a secondary output

commit f814c5dc9 changed get_output_work_area behaviour
which broke the code for positioning maximized window.
The x position was set to 2*output->x instead of to output->x

fix https://bugs.freedesktop.org/show_bug.cgi?id=92357

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>
Reviewed-by: Derek Foreman <2f97e0f0bc172406aab8ccd42dab54c95bab8759@osg.samsung.com>

kwm81/weston,sir-murray/weston,krezovic/weston,Gnurou/weston,kwm81/weston,sir-murray/weston,krezovic/weston,Fantu/compositor-spice,Fantu/compositor-spice,giucam/weston,Fantu/compositor-spice,giucam/weston,Gnurou/weston