ALSA: ISA: Remove superfluous *_set_drvdata(NULL) calls

Similarly like the previous commit for PCI drivers, remove
dev_set_drvdata(NULL) and pnp_set_drvdata(NULL) calls in ISA drivers
now.

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

sound/isa/gus/gusmax.c

@@ -357,7 +357,6 @@ static int snd_gusmax_probe(struct device *pdev, unsigned int dev)
 static int snd_gusmax_remove(struct device *devptr, unsigned int dev)
 {
 	snd_card_free(dev_get_drvdata(devptr));
-	dev_set_drvdata(devptr, NULL);
 	return 0;
 }