ALSA: virmidi: Fix wrong error check

While rewriting the code in the previous commit [316638a5: ALSA:
virmidi: fixed code style issues], the error check was wrongly
converted.  This resulted an Oops.

Fixes: 316638a5 ('ALSA: virmidi: fixed code style issues')
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/virmidi.c

@@ -121,7 +121,7 @@ static int snd_virmidi_probe(struct platform_device *devptr)
 	sprintf(card->longname, "Virtual MIDI Card %i", dev + 1);
 
 	err = snd_card_register(card);
-	if (err) {
+	if (!err) {
 		platform_set_drvdata(devptr, card);
 		return 0;
 	}