HID: multitouch: warn on sysfs group creation failure

This adds a warning message stating that the sysfs group was not able to be
created for the passed hid_device structure pointer with dev_warn.

Signed-off-by: Nicholas Krause <[e-mail]>
Reviewed-by: Benjamin Tissoires <[e-mail]>
[[e-mail]: massaged changelog a bit]
[[e-mail]: reformatted source]
Signed-off-by: Jiri Kosina <[e-mail]>

drivers/hid/hid-multitouch.c

···
 		return ret;
 
 	ret = sysfs_create_group(&hdev->dev.kobj, &mt_attribute_group);
+	if (ret)
+		dev_warn(&hdev->dev, "Cannot allocate sysfs group for %s\n",
+				hdev->name);
 
 	mt_set_maxcontacts(hdev);
 	mt_set_input_mode(hdev);