ALSA: enable build of snd-msnd-* drivers

Added the missing msnd directory to Makefile.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/isa/Makefile

@@ -26,5 +26,5 @@ obj-$(CONFIG_SND_SC6000) += snd-sc6000.o
 obj-$(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/