syscalls/splice02: Cleanup

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
syscalls/splice01: Cleanup & fixes.

* Use tst_exit() instead of return (0)
  (the possible test failure is propagated now)

* Use SAFE_MACROS()

* Remove useless comments

* ...

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>