Renamed atomic functions to match SDL 3.0 naming convention

This will also allow us to cleanly add atomic operations for other types in the future.

src/camera/v4l2/SDL_camera_v4l2.c

@@ -112,7 +112,7 @@ static bool V4L2_WaitDevice(SDL_Camera *device)
         }
 
         // Thread is requested to shut down
-        if (SDL_AtomicGet(&device->shutdown)) {
+        if (SDL_GetAtomicInt(&device->shutdown)) {
             return true;
         }