Smack: fix smack_new_inode bogosities

In January of 2012 Al Viro pointed out three bits of code that
he titled "new_inode_smack bogosities". This patch repairs these
errors.

1. smack_sb_kern_mount() included a NULL check that is impossible.
   The check and NULL case are removed.
2. smack_kb_kern_mount() included pointless locking. The locking is
   removed. Since this is the only place that lock was used the lock
   is removed from the superblock_smack structure.
3. smk_fill_super() incorrectly and unnecessarily set the Smack label
   for the smackfs root inode. The assignment has been removed.

Targeted for git://gitorious.org/smack-next/kernel.git



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