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

These two common macros will be no longer present everywhere.
Call out the include needs of them explicitly where required.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/drivers/mtd/nand/nand_bbt.c b/drivers/mtd/nand/nand_bbt.c
index ccbeaa1..4165857 100644
--- a/drivers/mtd/nand/nand_bbt.c
+++ b/drivers/mtd/nand/nand_bbt.c
@@ -67,6 +67,7 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/vmalloc.h>
+#include <linux/export.h>
 
 static int check_pattern_no_oob(uint8_t *buf, struct nand_bbt_descr *td)
 {