src: fix compiler warnings in node_perf.cc

Currently, there are a few compiler warnings generated from node_perf.cc regarding unused return values:

../src/node_perf.cc:58:3: warning: ignoring return value of function
declared with warn_unused_result attribute [-Wunused-result]
  env->performance_entry_callback()->Call(context,
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~
../src/node_perf.cc:293:5: warning: ignoring return value of function
declared with warn_unused_result attribute [-Wunused-result]
    obj->Set(context, idx, args[idx]);
    ^~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~
../src/node_perf.cc:373:3: warning: ignoring return value of function
declared with warn_unused_result attribute [-Wunused-result]
  target->DefineOwnProperty(context,
  ^~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~
../src/node_perf.cc:378:3: warning: ignoring return value of function
declared with warn_unused_result attribute [-Wunused-result]
  target->DefineOwnProperty(context,
  ^~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~

This commit add checks to avoid the warnings.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)