rp/pio: make sure gpio() asserts are compiled out

we'll have to touch pio one way or other if the number of gpio pins ever
increases. may as well make sure an assert never fires until that happens.

embassy-rp/src/pio.rs

@@ -1070,7 +1070,8 @@ fn on_pio_drop<PIO: Instance>() {
     if state.users.fetch_sub(1, Ordering::AcqRel) == 1 {
         let used_pins = state.used_pins.load(Ordering::Relaxed);
         let null = Gpio0ctrlFuncsel::NULL.0;
-        for i in 0..32 {
+        // we only have 30 pins. don't test the other two since gpio() asserts.
+        for i in 0..30 {
             if used_pins & (1 << i) != 0 {
                 unsafe {
                     pac::IO_BANK0.gpio(i).ctrl().write(|w| w.set_funcsel(null));