selinux: Don't sleep inside inode_getsecid hook

The inode_getsecid hook is called from contexts in which sleeping is not
allowed, so we cannot revalidate inode security labels from there. Use
the non-validating version of inode_security() instead.

Reported-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>