[MTD][MTDPART] Handle most checkpatch findings

Remaining are 12 warnings about long lines and 1 about braces that
could be argued about.

Signed-off-by: Jörn Engel <joern@logfs.org>
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>