callback: Change resource to a wl_resource pointer
callback: Change resource to a wl_resource pointer

Signed-off-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

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