[ALSA] fix SND_CS5530=y, ISA=n compilation

This patch fixes the following compile error with
CONFIG_SND_CS5530=y, CONFIG_ISA=n:
<--  snip  -->
...
  LD      .tmp_vmlinux1
sound/built-in.o: In function 'snd_sb16_capture_trigger':
sb16_main.c:(.text+0x212ad): undefined reference to 'snd_sbdsp_command'
sb16_main.c:(.text+0x212cc): undefined reference to 'snd_sbdsp_command'
sb16_main.c:(.text+0x212f7): undefined reference to 'snd_sbdsp_command'
sound/built-in.o: In function 'snd_sb16_playback_trigger':
sb16_main.c:(.text+0x2136d): undefined reference to 'snd_sbdsp_command'
sb16_main.c:(.text+0x2138c): undefined reference to 'snd_sbdsp_command'
...
<--  snip  -->

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>