ALSA: doc: my_chip has no element ioport

chip->ioport is dereferenced in two places, but the struct is
defined as follows:

struct mychip {
	struct snd_card *card;
	struct pci_dev *pci;

	unsigned long port;
	int irq;
};

Signed-off-by: Christina Quast <cquast@hanoverdisplays.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>