mtd: omap2: use msecs_to_jiffies()

Fix mtd-utils from returning -EIO. Formatting jffs2 filesystem was impossible
when CONFIG_HZ was set to a low value.

Signed-off-by: Toan Pham <tpham3783@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>