compositor: Tweak fade spring to not overshoot
compositor: Tweak fade spring to not overshoot

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