locking/static_keys: Fix a silly typo

locking/static_keys: Fix a silly typo

Commit:

  412758cb2670 ("jump label, locking/static_keys: Update docs")

introduced a typo that might as well get fixed.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150907131803.54c027e1@lwn.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>