ALSA: atmel: ac97c: fix error return code in atmel_ac97c_probe()

platform_get_irq() returns an error code, but the ac97c
driver ignores it and always returns -ENXIO. This is not correct,
and prevents -EPROBE_DEFER from being propagated properly.
Notice that platform_get_irq() no longer returns 0 on error.

Print and propagate the return value of platform_get_irq on failure.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>