sound examples: Move MIDI example out of OSS directory

This example is not related to OSS.

Sponsored by:	The FreeBSD Foundation
MFC after:	2 days
Reviewed by:	dev_submerge.ch, meka_tilda.center
Differential Revision:	https://reviews.freebsd.org/D46308

share/examples/Makefile

@@ -315,13 +315,13 @@ SE_SCSI_TARGET= \
 
 SE_DIRS+=	sound
 SE_SOUND= \
-	  sndstat_nv.c
+	  sndstat_nv.c \
+	  midi.c
 
 SE_DIRS+=	sound/oss
 SE_SOUND_OSS= \
 	README \
-	audio.c \
-	midi.c
+	audio.c
 
 SE_DIRS+=	sunrpc
 SE_SUNRPC=	Makefile