rv: Set variable 'da_mon_##name' to static

gcc with W=1 reports
kernel/trace/rv/monitors/wip/wip.c:20:1: sparse: sparse: symbol 'da_mon_wip' was not declared. Should it be static?

The per-cpu variable 'da_mon_##name' is only used in its defining file, so
it should be static.

Link: https://lore.kernel.org/linux-trace-kernel/20230823020051.3184953-1-liaoyu15@huawei.comReported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202307280030.7EjUG9gR-lkp@intel.com/Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/rv/da_monitor.h

@@ -262,7 +262,7 @@ static inline void da_monitor_destroy_##name(void)						\
 /*												\
  * per-cpu monitor variables									\
  */												\
-DEFINE_PER_CPU(struct da_monitor, da_mon_##name);						\
+static DEFINE_PER_CPU(struct da_monitor, da_mon_##name);					\
 												\
 /*												\
  * da_get_monitor_##name - return current CPU monitor address					\