various: remove redundant return

void return type functions don't need a final return statement.

filters/f_hwtransfer.c

@@ -654,7 +654,6 @@ static void hwdownload_process(struct mp_filter *f)
 
 passthrough:
     mp_pin_in_write(f->ppins[1], frame);
-    return;
 }
 
 static const struct mp_filter_info hwdownload_filter = {

filters/f_lavfi.c

@@ -311,7 +311,6 @@ static void precreate_graph(struct lavfi *c, bool first_init)
 error:
     free_graph(c);
     c->failed = true;
-    return;
 }
 
 // Ensure to send EOF to each input pad, so the graph can be drained properly.

filters/f_swscale.c

@@ -125,7 +125,6 @@ static void sws_process(struct mp_filter *f)
 error:
     mp_frame_unref(&frame);
     mp_filter_internal_mark_failed(f);
-    return;
 }
 
 static const struct mp_filter_info sws_filter = {