sound: Correct data output in sound_create_square_wave()

This function currently outputs twice as much data as it should and
overwrites its buffer as a result. Fix it.
Signed-off-by: NSimon Glass <sjg@chromium.org>

drivers/sound/sound.c

@@ -25,12 +25,10 @@ void sound_create_square_wave(unsigned short *data, int size, uint32_t freq)
 		for (i = 0; size && i < half; i++) {
 			size -= 2;
 			*data++ = amplitude;
-			*data++ = amplitude;
 		}
 		for (i = 0; size && i < period - half; i++) {
 			size -= 2;
 			*data++ = -amplitude;
-			*data++ = -amplitude;
 		}
 	}
 }