[ALSA] fix section mismatch

Fix shared init/exit function attributes:
WARNING: sound/built-in.o(.exit.text+0x4a1): Section mismatch: reference to .init.text: (between 'alsa_card_virmidi_exit' and 'alsa_card_serial_exit')
WARNING: sound/built-in.o(.exit.text+0x4c1): Section mismatch: reference to .init.text: (between 'alsa_card_serial_exit' and 'ac97_bus_exit')

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

sound/drivers/serial-u16550.c

@@ -998,7 +998,7 @@ static struct platform_driver snd_serial_driver = {
 	},
 };
 
-static void __init_or_module snd_serial_unregister_all(void)
+static void snd_serial_unregister_all(void)
 {
 	int i;
 

sound/drivers/virmidi.c

@@ -145,7 +145,7 @@ static struct platform_driver snd_virmidi_driver = {
 	},
 };
 
-static void __init_or_module snd_virmidi_unregister_all(void)
+static void snd_virmidi_unregister_all(void)
 {
 	int i;