title: Checked attribute not working in mat-radio-button
body: <p>I am creating a radio button with the checked property but it's not showing selected</p>
  
  <pre><code>&lt;mat-radio-group name="radioOpt1" [(ngModel)]="selectedRadio" [ngModelOptions]="{standalone: true}" (change)="radioChange($event)"&gt;
  &lt;mat-radio-button value="own" checked name="own"&gt;Own&lt;/mat-radio-button&gt;
  &lt;mat-radio-button value="competitor" name="own"&gt;competitor&lt;/mat-radio-button&gt; &lt;/mat-radio-group&gt;
  </code></pre>
  
  <p>I want the first radio button to be checked by default</p>