sched, timer: Fix documentation for 'struct thread_group_cputimer'

Fix the docbook build bug reported by Fengguang Wu.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NJason Low <jason.low2@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman.Long@hp.com
Cc: aswin@hp.com
Cc: bp@alien8.de
Cc: dave@stgolabs.net
Cc: fweisbec@gmail.com
Cc: mgorman@suse.de
Cc: oleg@redhat.com
Cc: paulmck@linux.vnet.ibm.com
Cc: preeti@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: rostedt@goodmis.org
Cc: scott.norton@hp.com
Cc: torvalds@linux-foundation.org
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/1431120710.5136.12.camel@j-VirtualBoxSigned-off-by: NIngo Molnar <mingo@kernel.org>

include/linux/sched.h

@@ -606,10 +606,9 @@ struct task_cputime_atomic {
 
 /**
  * struct thread_group_cputimer - thread group interval timer counts
- * @cputime:		thread group interval timers.
+ * @cputime_atomic:	atomic thread group interval timers.
  * @running:		non-zero when there are timers running and
  * 			@cputime receives updates.
- * @lock:		lock for fields in this struct.
  *
  * This structure contains the version of task_cputime, above, that is
  * used for thread group CPU timer calculations.