Smack: correct final mmap check comparison

Smack: correct final mmap check comparison

The mmap policy enforcement checks the access of the
SMACK64MMAP subject against the current subject incorrectly.
The check as written works correctly only if the access
rules involved have the same access. This is the common
case, so initial testing did not find a problem.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>