ALSA: move snd_powermac's probe function to .devinit.text

A pointer to snd_pmac_probe is passed to the core via
platform_driver_register and so the function must not disappear when the
.init sections are discarded.  Otherwise (when having HOTPLUG=y)
unbinding and binding a device to the driver via sysfs will result in an
oops as does a device being registered late.

An alternative to this patch is using platform_driver_probe instead of
platform_driver_register plus removing the pointer to the probe function
from the struct platform_driver.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Rene Herman <rene.herman@keyaccess.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>