directwrite: fix compilation
directwrite: fix compilation

A name clash was introduced by commit ab08d079.

stps/libass,Akemi/libass,libass/libass,xbmc/libass,torque/libass,astiob/libass,grigorig/libass,stps/libass,MrSmile/libass,stps/libass,MrSmile/libass,ShiftMediaProject/libass,sanyaade-g2g-repos/libass,mwgoldsmith/libass,Akemi/libass,mwgoldsmith/libass,libass/libass,torque/libass,xbmc/libass,mwgoldsmith/libass,ShiftMediaProject/libass,astiob/libass,grigorig/libass,Akemi/libass,sanyaade-g2g-repos/libass,torque/libass,sanyaade-g2g-repos/libass