[ALSA] Fix __devinit and __devexit issues with sound drivers

Fix __devinit and __devexit issues with sound drivers.
Resolves MODPOST warnings similar to:
WARNING: sound/drivers/snd-dummy.o - Section mismatch: reference to .init.text:snd_dummy_probe from .data.rel.local between 'snd_dummy_driver' (at offset 0x0) and 'snd_dummy_controls'
WARNING: sound/drivers/snd-mtpav.o - Section mismatch: reference to .init.text:snd_mtpav_probe from .data.rel.local between 'snd_mtpav_driver' (at offset 0x0) and 'snd_mtpav_input'
WARNING: sound/drivers/snd-virmidi.o - Section mismatch: reference to .init.text:snd_virmidi_probe from .data.rel.local after 'snd_virmidi_driver' (at offset 0x0)

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>