mtd: nand: nand_bbt: export nand_update_bbt

When building MTD_NAND_GPMI_NAND as module, the following error shows up:

ERROR: "nand_update_bbt" [drivers/mtd/nand/gpmi-nand/gpmi_nand.ko] undefined!

Export nand_update_bbt to fix it.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/nand_bbt.c

@@ -4,7 +4,7 @@
  *  Overview:
  *   Bad block table support for the NAND driver
  *
- *  Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
+ *  Copyright © 2004 Thomas Gleixner (tglx@linutronix.de)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -1404,3 +1404,4 @@ int nand_isbad_bbt(struct mtd_info *mtd, loff_t offs, int allowbbt)
 
 EXPORT_SYMBOL(nand_scan_bbt);
 EXPORT_SYMBOL(nand_default_bbt);
+EXPORT_SYMBOL_GPL(nand_update_bbt);