smack: Fix gcc warning from unused smack_syslog_lock mutex in smackfs.c

In commit 00f84f3f2e9d088f06722f4351d67f5f577abe22 ("Smack: Make the
syslog control configurable") this mutex was added, but the rest of
the final commit never actually made use of it, resulting in:

In file included from include/linux/mutex.h:29:0,
from include/linux/notifier.h:13,
from include/linux/memory_hotplug.h:6,
from include/linux/mmzone.h:821,
from include/linux/gfp.h:5,
from include/linux/slab.h:14,
from include/linux/security.h:27,
from security/smack/smackfs.c:21:
security/smack/smackfs.c:63:21: warning: ‘smack_syslog_lock’ defined but not used [-Wunused-variable]
static DEFINE_MUTEX(smack_syslog_lock);
^

A git grep shows no other instances/references to smack_syslog_lock.
Delete it, assuming that the mutex addition was just a leftover from
an earlier work in progress version of the change.

Signed-off-by: Paul Gortmaker <[e-mail]>

security/smack/smackfs.c

···
  */
 static DEFINE_MUTEX(smack_cipso_lock);
 static DEFINE_MUTEX(smack_ambient_lock);
-static DEFINE_MUTEX(smack_syslog_lock);
 static DEFINE_MUTEX(smk_netlbladdr_lock);
 
 /*