staging: dgrp: dgrp_tty.c: Audit the return values of get/put_user()

fix for missing audits for return values of get_user() and put_user().
Inspecting the return values of get/put_user() would make the access_ok()
redundant, hence removing calls to access_ok() in such scenarios.

Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>