ptrace: cleanup arch_ptrace() on h8300

Use new 'regno', 'datap' variables in order to remove duplicated
expressions and unnecessary castings. Alse remove checking @addr
less than 0 because addr is now unsigned.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>