test/vtophys: reduce amount of memory requested

There is no reason for this test to consume all of
the huge pages on the system.  256MB is sufficient.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Id1813f4ff6a1fdd1d65fdcc76f6919f6e73b988f

Reviewed-on: https://review.gerrithub.io/420309
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
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>

test/env/vtophys/vtophys.c

@@ -155,6 +155,7 @@ main(int argc, char **argv)
 	spdk_env_opts_init(&opts);
 	opts.name = "vtophys";
 	opts.core_mask = "0x1";
+	opts.mem_size = 256;
 	if (spdk_env_init(&opts) < 0) {
 		printf("Err: Unable to initialize SPDK env\n");
 		return 1;