mtd: mtdcore: remove unnecessary mtd->resume check

We don't need to to check for mtd->resume before calling mtd_resume().
mtd_resume() should take care of that.

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>