remove stray snd_pcm_prepare() call from alsapcm_write()

this came from 438e52e, which tried to partially revert c2a6b6e, but
inserted a chunk that actually belonged to alsapcm_drop(). the latter
does not need to be restored, as we now handle SND_PCM_STATE_SETUP prior
to reading/writing.

alsaaudio.c

@@ -1495,8 +1495,7 @@ static PyObject *alsapcm_write(alsapcm_t *self, PyObject *args)
 	if (res == -EAGAIN) {
 		rc = PyLong_FromLong(0);
 	}
-	res = snd_pcm_prepare(self->handle);
-	if (res < 0)
+	else if (res < 0)
 	{
 		PyErr_Format(ALSAAudioError, "%s [%s]", snd_strerror(res),
 					 self->cardname);