image-source: Correctly assign hotkey to next instead of prev

plugins/image-source/obs-slideshow.c

@@ -654,7 +654,7 @@ static void *ss_create(obs_data_t *settings, obs_source_t *source)
 		source, "SlideShow.Stop", obs_module_text("SlideShow.Stop"),
 		stop_hotkey, ss);
 
-	ss->prev_hotkey = obs_hotkey_register_source(
+	ss->next_hotkey = obs_hotkey_register_source(
 		source, "SlideShow.NextSlide",
 		obs_module_text("SlideShow.NextSlide"), next_slide_hotkey, ss);