mtd: remove dead non-char logic

MTD used to allow compiling out character device support. This was
dropped in the following commit, but some of the accompanying logic was
never dropped:

  commit 660685d9
  Author: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
  Date:   Thu Mar 14 13:27:40 2013 +0200

      mtd: merge mtdchar module with mtdcore

The weird logic was flagged by Coverity.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>