percpu: fix generic definition of __this_cpu_add_and_return()

This patch adds missed "__" into function prefix.
Otherwise on all archectures (except x86) it expands to irq/preemtion-safe
variant: _this_cpu_generic_add_return(), which do extra irq-save/irq-restore.
Optimal generic implementation is __this_cpu_generic_add_return().
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

include/linux/percpu.h

@@ -718,7 +718,8 @@ do {									\
 # ifndef __this_cpu_add_return_8
 #  define __this_cpu_add_return_8(pcp, val)	__this_cpu_generic_add_return(pcp, val)
 # endif
-# define __this_cpu_add_return(pcp, val)	__pcpu_size_call_return2(this_cpu_add_return_, pcp, val)
+# define __this_cpu_add_return(pcp, val)	\
+	__pcpu_size_call_return2(__this_cpu_add_return_, pcp, val)
 #endif
 
 #define __this_cpu_sub_return(pcp, val)	this_cpu_add_return(pcp, -(val))