ALSA: mpu401: Remove redundant platform_set_drvdata()

Commit 0998d06310 (device-core: Ensure drvdata = NULL when no
driver is bound) removes the need to set driver data field to
NULL.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/mpu401/mpu401.c

@@ -129,7 +129,6 @@ static int snd_mpu401_probe(struct platform_device *devptr)
 static int snd_mpu401_remove(struct platform_device *devptr)
 {
 	snd_card_free(platform_get_drvdata(devptr));
-	platform_set_drvdata(devptr, NULL);
 	return 0;
 }