ptrace: cleanup arch_ptrace() on mn10300

Use new 'datap' variable in order to remove unnecessary castings.
Also remove checking @addr less than 0 because @addr is now unsigned.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>