Fixed warning C4389: '!=': signed/unsigned mismatch in SDL_blit.c

src/video/SDL_blit.h

@@ -79,7 +79,7 @@ typedef struct
     Uint32 src_format;
     Uint32 dst_format;
     int flags;
-    int cpu;
+    unsigned int cpu;
     SDL_BlitFunc func;
 } SDL_BlitFuncEntry;