selinux: fix error initialization in inode_doinit_with_dentry()

[ Upstream commit 83370b31a915493231e5b9addc72e4bef69f8d31 ]

Mark the inode security label as invalid if we cannot find
a dentry so that we will retry later rather than marking it
initialized with the unlabeled SID.

Fixes: 9287aed2 ("selinux: Convert isec->lock into a spinlock")
Signed-off-by: Tianyue Ren <rentianyue@kylinos.cn>
[PM: minor comment tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>