ALSA: enable build of snd-msnd-* drivers

Added the missing msnd directory to Makefile.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/isa/Makefile b/sound/isa/Makefile
index 63af13d..b906b9a 100644
--- a/sound/isa/Makefile
+++ b/sound/isa/Makefile
@@ -26,5 +26,5 @@
 obj-$(CONFIG_SND_SGALAXY) += snd-sgalaxy.o
 obj-$(CONFIG_SND_SSCAPE) += snd-sscape.o
 
-obj-$(CONFIG_SND) += ad1816a/ ad1848/ cs423x/ es1688/ gus/ opti9xx/ \
+obj-$(CONFIG_SND) += ad1816a/ ad1848/ cs423x/ es1688/ gus/ msnd/ opti9xx/ \
 		     sb/ wavefront/ wss/