smack: make smk_cipso_doi() and smk_unlbl_ambient()

The functions smk_cipso_doi and smk_unlbl_ambient are not used outside
smackfs.c and should hence be static.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>