usb: gadget: u_uac1: Kill set_fs() usage

With the new API to perform the in-kernel buffer copy, we can get rid
of set_fs() usage in this driver, finally.
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: NTakashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

drivers/usb/gadget/function/u_uac1.c

@@ -157,7 +157,6 @@ size_t u_audio_playback(struct gaudio *card, void *buf, size_t count)
 	struct gaudio_snd_dev	*snd = &card->playback;
 	struct snd_pcm_substream *substream = snd->substream;
 	struct snd_pcm_runtime *runtime = substream->runtime;
-	mm_segment_t old_fs;
 	ssize_t result;
 	snd_pcm_sframes_t frames;
 
@@ -174,15 +173,11 @@ size_t u_audio_playback(struct gaudio *card, void *buf, size_t count)
 	}
 
 	frames = bytes_to_frames(runtime, count);
-	old_fs = get_fs();
-	set_fs(KERNEL_DS);
-	result = snd_pcm_lib_write(snd->substream, (void __user *)buf, frames);
+	result = snd_pcm_kernel_write(snd->substream, buf, frames);
 	if (result != frames) {
 		ERROR(card, "Playback error: %d\n", (int)result);
-		set_fs(old_fs);
 		goto try_again;
 	}
-	set_fs(old_fs);
 
 	return 0;
 }