mtd: adjust kernel-docs to avoid Sphinx/kerneldoc warnings

./drivers/mtd/nand/nand_bbt.c:1: warning: no structured comments found
./include/linux/mtd/nand.h:785: ERROR: Unexpected indentation.
./drivers/mtd/nand/nand_base.c:449: WARNING: Definition list ends without a blank line; unexpected unindent.
./drivers/mtd/nand/nand_base.c:1161: ERROR: Unexpected indentation.
./drivers/mtd/nand/nand_base.c:1162: WARNING: Block quote ends without a blank line; unexpected unindent.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 9591e0f..3d5b203 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -779,7 +779,7 @@
  *			Minimum amount of bit errors per @ecc_step_ds guaranteed
  *			to be correctable. If unknown, set to zero.
  * @ecc_step_ds:	[INTERN] ECC step required by the @ecc_strength_ds,
- *                      also from the datasheet. It is the recommended ECC step
+ *			also from the datasheet. It is the recommended ECC step
  *			size, if known; if unknown, set to zero.
  * @onfi_timing_mode_default: [INTERN] default ONFI timing mode. This field is
  *			      set to the actually used ONFI mode if the chip is