locking/static_keys: Fix up the static keys documentation

locking/static_keys: Fix up the static keys documentation

Fix a few small mistakes in the static key documentation and
delete an unneeded sentence.

Suggested-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150914171105.511e1e21@lwn.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1975dbc276c6ab62230cf4f9df5ddc9ff0e0e473)

Orabug: 28607548

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>