Fix -Wundef warnings due to use of unguarded SDL_VIDEO_DRIVER_PS2

src/video/SDL_video.c

@@ -91,7 +91,7 @@ static VideoBootStrap *bootstrap[] = {
 #ifdef SDL_VIDEO_DRIVER_ANDROID
     &Android_bootstrap,
 #endif
-#if SDL_VIDEO_DRIVER_PS2
+#ifdef SDL_VIDEO_DRIVER_PS2
     &PS2_bootstrap,
 #endif
 #if SDL_VIDEO_DRIVER_PSP

src/video/ps2/SDL_ps2video.c

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-#if SDL_VIDEO_DRIVER_PS2
+#ifdef SDL_VIDEO_DRIVER_PS2
 
 /* PS2 SDL video driver implementation; this is just enough to make an
  *  SDL-based application THINK it's got a working video driver, for