audiocore: Fix race window in i2s_stop

Apply the same pattern as in 6f155ebb55 ("audiocore: Fix small race
window in get_fifo_read_value_blocking") and 2a4033d3ca ("rp2_sd: Fix
race window in sd_spi_wait_complete") to the wait for interrupt in
i2s_stop too.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>

software/modules/audiocore/i2s.c

@@ -91,19 +91,21 @@ void i2s_stop(void)
 {
     if (!i2s_context.playback_active)
         return;
-    bool have_data = false;
+    while (true) {
-    do {
         const long flags = save_and_disable_interrupts();
         const int next_buf = (i2s_context.cur_playing + 1) % AUDIO_BUFS;
-        have_data = i2s_context.has_data[next_buf];
+        const bool have_data = i2s_context.has_data[next_buf];
-        restore_interrupts(flags);
+        if (!have_data) {
-        if (have_data)
-            __wfi();
-    } while (have_data);
-    const long flags = save_and_disable_interrupts();
             i2s_context.playback_active = false;
             shared_context.underruns = 0;
             restore_interrupts(flags);
+            break;
+        }
+        __wfi();
+        restore_interrupts(flags);
+        __nop(); // Ensure at least two instructions between enable interrupts and subsequent disable
+        __nop();
+    }
     // Workaround rp2040 E13
     dma_channel_set_irq1_enabled(i2s_context.dma_ch, false);
     dma_channel_abort(i2s_context.dma_ch);