[ALSA] make snd-powermac load even when it can't bind the device

This patch makes snd-powermac load when it can't bind the device right
away. That's the expected behaviour for hotplugging, but fixes an
important problem I was seeing with doing a modprobe snd-powermac with
a version that refuses loading on machines with layout-id: snd-powermac
would create a bunch of uevents and then refuse to load, the uevents
causing udev to reload it again, ad eternum.

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