[ALSA] wavefront: only declare isapnp on CONFIG_PNP

From: David Rientjes <rientjes@google.com>
isapnp[] is only used for CONFIG_PNP.  If this configuration option is
not set, do not declare the array.
Cc: Adam Belay <ambx1@neo.rr.com>
Cc: Takashi Iwai <tiwai@suse.de>

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>