window: use different keys for different cairo privates
window: use different keys for different cairo privates

cairo_surface_t objects have a private set, either struct
shm_surface_data, or struct egl_window_surface_data. Use separate
private keys for each type to avoid mismatch.

This makes display_get_buffer_for_surface() safe, in that it won't
return garbage for an EGL-based cairo surface.

Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

jonnylamb/weston,Fantu/compositor-spice,Fantu/compositor-spice,krezovic/weston,xorgy/weston,kwm81/weston,eyolfson/weston,mchalupa/weston,Tarnyko/weston-xdg_surface_present,sir-murray/weston,krezovic/weston,Gnurou/weston,xorgy/weston,kwm81/weston,udoprog/weston,Fantu/compositor-spice,giucam/weston,Tarnyko/weston-xdg_surface_present,giucam/weston,Gnurou/weston,sir-murray/weston,udoprog/weston,jonnylamb/weston,eyolfson/weston,mchalupa/weston