[ALSA] portman2x4 section mismatch

FIx section mismatch when CONFIG_HOTPLUG=n:
WARNING: sound/built-in.o(.exit.text+0x271): Section mismatch: reference to .init.text:snd_p
ortman_unregister_all (between 'snd_portman_module_exit' and 'alsa_mpu401_uart_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>