splash: Print error message when no renderer is found

the splash command silently fails when no renderer is found for
an image type. Print an error message in this case.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

lib/gui/image_renderer.c

@@ -23,6 +23,8 @@ static struct image_renderer *get_renderer(void* buf, size_t bufsize)
 			return ir;
 	}
 
+	eprintf("No renderer found for filetype %s\n", file_type_to_string(type));
+
 	return NULL;
 }