mtd: rawnand: Update dead URL

The current link to the ONFI specification is broken, the onfi.org
website now points to materials on Micron's website. Update the URL
accordingly.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-6-miquel.raynal@bootlin.com

include/linux/mtd/rawnand.h

@@ -385,8 +385,8 @@ struct nand_ecc_ctrl {
  * This struct defines the timing requirements of a SDR NAND chip.
  * These information can be found in every NAND datasheets and the timings
  * meaning are described in the ONFI specifications:
- * www.onfi.org/~/media/ONFI/specs/onfi_3_1_spec.pdf (chapter 4.15 Timing
- * Parameters)
+ * https://media-www.micron.com/-/media/client/onfi/specs/onfi_3_1_spec.pdf
+ * (chapter 4.15 Timing Parameters)
  *
  * All these timings are expressed in picoseconds.
  *