sound: Add export.h for THIS_MODULE/EXPORT_SYMBOL where needed

These aren't modules, but they do make use of these macros, so
they will need export.h to get that definition.  Previously,
they got it via the implicit module.h inclusion.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

sound/drivers/opl3/opl3_oss.c

@@ -18,6 +18,7 @@
  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  */
 
+#include <linux/export.h>
 #include "opl3_voice.h"
 
 static int snd_opl3_open_seq_oss(struct snd_seq_oss_arg *arg, void *closure);