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>
diff --git a/sound/pci/emu10k1/io.c b/sound/pci/emu10k1/io.c
index 5ef7080..e4fba49 100644
--- a/sound/pci/emu10k1/io.c
+++ b/sound/pci/emu10k1/io.c
@@ -29,6 +29,7 @@
 #include <sound/core.h>
 #include <sound/emu10k1.h>
 #include <linux/delay.h>
+#include <linux/export.h>
 #include "p17v.h"
 
 unsigned int snd_emu10k1_ptr_read(struct snd_emu10k1 * emu, unsigned int reg, unsigned int chn)