shell: fix set_transient

In the wl_shell_surface migration, I forgot to correct one cast in
shell_surface_set_transient(). 'parent_resource' is not a (struct
wlsc_surface *) but (struct shell_surface *).

This bug corrupts a wlsc_surface::output field, which later (in my
experiments) leads to a segmentation fault in surface_frame().

Fix the casts.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
1 file changed