ALSA: sscape: add missing include of linux/io.h

The soundscape driver uses the ISA inb/outb functions declared
in linux/io.h, so it needs to include this header to avoid
a build error:

sscape.c: In function 'sscape_write_unsafe':
sscape.c:203:2: error: implicit declaration of function 'outb' [-Werror=implicit-function-declaration]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>