mtd: nand: fix DocBook warnings on nand_sdr_timings doc

Change the comment type (from /** to /*) to prevent DocBook from
complaining about missing description for nand_sdr_timings fields.

There is currently no need in documenting those fields because they are
fully described in the ONFI specification (which is pointed out in the
comment).

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

include/linux/mtd/nand.h

@@ -949,7 +949,7 @@ static inline int jedec_feature(struct nand_chip *chip)
 		: 0;
 }
 
-/**
+/*
  * struct nand_sdr_timings - SDR NAND chip timings
  *
  * This struct defines the timing requirements of a SDR NAND chip.