test/event_perf: use less memory

There's no reason this test needs to use all of the
hugepage memory allocated in the system.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Iab575d322f2d1cb6452e5ebd7705aee9353a6fba

Reviewed-on: https://review.gerrithub.io/420456
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>

test/event/event_perf/event_perf.c

@@ -144,6 +144,7 @@ main(int argc, char **argv)
 	int rc = 0;
 
 	opts.name = "event_perf";
+	opts.mem_size = 256;
 
 	g_time_in_sec = 0;