ALSA: rawmidi: A lightweight function to discard pending bytes

For discarding the pending bytes on rawmidi, we process with a loop of
snd_rawmidi_transmit() which is just a waste of CPU power.
Implement a lightweight API function to discard the pending bytes and
the proceed the ring buffer instantly, and use it instead of open
codes.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/seq_virmidi.c

@@ -149,9 +149,7 @@ static void snd_vmidi_output_work(struct work_struct *work)
 	/* discard the outputs in dispatch mode unless subscribed */
 	if (vmidi->seq_mode == SNDRV_VIRMIDI_SEQ_DISPATCH &&
 	    !(vmidi->rdev->flags & SNDRV_VIRMIDI_SUBSCRIBE)) {
-		char buf[32];
-		while (snd_rawmidi_transmit(substream, buf, sizeof(buf)) > 0)
-			; /* ignored */
+		snd_rawmidi_proceed(substream);
 		return;
 	}