[ALSA] aoa: feature gpio layer: fix IRQ access

The IRQ rework caused some hiccups here, in some cases we call
get_irq without a device node. This patch makes it catch that
case and return NO_IRQ when it happens, along with changing the
place where the irq is checked to check for NO_IRQ instead of -1.
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>