md: Add in export.h for files using EXPORT_SYMBOL

These files were getting the defines for EXPORT_SYMBOL because
device.h was including module.h.  But we are going to put an
end to that.  So add the proper export.h include now.

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

lib/raid6/recov.c

@@ -18,6 +18,7 @@
  * the syndrome.)
  */
 
+#include <linux/export.h>
 #include <linux/raid/pq.h>
 
 /* Recover two failed data blocks. */