ALSA: hda - Add missing inclusion of linux/export.h

This is needed newly since 3.2...

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/hda/hda_jack.c b/sound/pci/hda/hda_jack.c
index e014562..25f7565 100644
--- a/sound/pci/hda/hda_jack.c
+++ b/sound/pci/hda/hda_jack.c
@@ -11,6 +11,7 @@
 
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/export.h>
 #include <sound/core.h>
 #include <sound/control.h>
 #include <sound/jack.h>