x86, wmi fix modalias_show return values

I just fixed this same bug in arch/powerpc/kernel/vio.c and took a quick
look for other similar errors in the kernel.

modalias_show() should return an empty string on error, not errno.
Signed-off-by: NPrarit Bhargava <prarit@redhat.com>
Cc: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: NMatthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/wmi.c

@@ -672,8 +672,10 @@ static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
 	struct wmi_block *wblock;
 
 	wblock = dev_get_drvdata(dev);
-	if (!wblock)
-		return -ENOMEM;
+	if (!wblock) {
+		strcat(buf, "\n");
+		return strlen(buf);
+	}
 
 	wmi_gtoa(wblock->gblock.guid, guid_string);