sys_pipe(): fix file descriptor leaks

Remember to close the files if copy_to_user() failed.

Spotted by dm.n9107@gmail.com.

Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Cc: DM <dm.n9107@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>