fix type redefinition error after commit dfe4445214

In file included from /tmp/SDL3/src/events/SDL_events_c.h:28,
                 from /tmp/SDL3/src/SDL.c:46:
/tmp/SDL3/src/events/../video/SDL_sysvideo.h:31: error: redefinition of typedef 'SDL_VideoDevice'
/tmp/SDL3/src/video/SDL_video_c.h:27: note: previous declaration of 'SDL_VideoDevice' was here

src/video/SDL_video_c.h

@@ -24,7 +24,7 @@
 
 #include "SDL_internal.h"
 
-typedef struct SDL_VideoDevice SDL_VideoDevice;
+struct SDL_VideoDevice;
 
 /**
  * Initialize the video subsystem, optionally specifying a video driver.
@@ -57,7 +57,7 @@ extern int SDL_VideoInit(const char *driver_name);
  */
 extern void SDL_VideoQuit(void);
 
-extern int SDL_SetWindowTextureVSync(SDL_VideoDevice *_this, SDL_Window *window, int vsync);
+extern int SDL_SetWindowTextureVSync(struct SDL_VideoDevice *_this, SDL_Window *window, int vsync);
 
 extern int SDL_ReadSurfacePixel(SDL_Surface *surface, int x, int y, Uint8 *r, Uint8 *g, Uint8 *b, Uint8 *a);