cramfs: only unlock new inodes

Commit 77b8a75f introduced a warning at fs/inode.c:692 unlock_new_inode(),
caused by unlock_new_inode() being called on existing inodes as well.

This patch changes setup_inode() to only call unlock_new_inode() for I_NEW
inodes.

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>