rcu: Update RCU maintainership

Drop Dipankar Sarma at his request (https://lkml.org/lkml/2014/6/2/628),
add Josh Triplett based on long-term review, contributions, and
agreement to take on this role (https://lkml.org/lkml/2014/6/2/554).
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

MAINTAINERS

@@ -7405,6 +7405,7 @@ F:	kernel/rcu/torture.c
 
 RCUTORTURE TEST FRAMEWORK
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
+M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
 R:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 R:	Lai Jiangshan <laijs@cn.fujitsu.com>
@@ -7430,8 +7431,8 @@ S:	Supported
 F:	net/rds/
 
 READ-COPY UPDATE (RCU)
-M:	Dipankar Sarma <dipankar@in.ibm.com>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
+M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
 R:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 R:	Lai Jiangshan <laijs@cn.fujitsu.com>
@@ -8214,6 +8215,7 @@ F:	mm/sl?b.c
 SLEEPABLE READ-COPY UPDATE (SRCU)
 M:	Lai Jiangshan <laijs@cn.fujitsu.com>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
+M:	Josh Triplett <josh@joshtriplett.org>
 R:	Steven Rostedt <rostedt@goodmis.org>
 R:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 L:	linux-kernel@vger.kernel.org