Explicitly declare function parameters for GCC 15 compatibility

In GCC 15, where C23 is the default, void foo() is equivalent to void
foo(void). Therefore, functions must explicitly declare their
parameters.

src/process_pipeline.c

@@ -1410,7 +1410,7 @@ mp_process_pipeline_process_image(MPBuffer buffer)
 }
 
 static void
-capture()
+capture(struct _MPPipeline *pipeline, const void *data)
 {
 	setup_capture();