mtd: fix nand kernel-doc warnings

Warning(include/linux/mtd/nand.h:543): No description found for parameter 'badblockbits'
Warning(drivers/mtd/nand/nand_bbt.c:1101): No description found for parameter 'mtd'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc:	David Woodhouse <dwmw2@infradead.org>
Cc:	linux-mtd@lists.infradead.org
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 63e17d0..1f489b2 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -448,6 +448,8 @@
  *			See the defines for further explanation.
  * @badblockpos:	[INTERN] position of the bad block marker in the oob
  *			area.
+ * @badblockbits:	[INTERN] number of bits to left-shift the bad block
+ *			number
  * @cellinfo:		[INTERN] MLC/multichip data from chip ident
  * @numchips:		[INTERN] number of physical chips
  * @chipsize:		[INTERN] the size of one chip for multichip arrays