Update input-prefix-suffix-example.html (#28423)

(cherry picked from commit 6c713b5)

Author: mohammedsahl

src/components-examples/material/input/input-prefix-suffix/input-prefix-suffix-example.html

@@ -1,7 +1,7 @@
 <form class="example-form">
   <mat-form-field class="example-full-width">
     <mat-label>Telephone</mat-label>
-    <span matPrefix>+1 &nbsp;</span>
+    <span matTextPrefix>+1 &nbsp;</span>
     <input type="tel" matInput placeholder="555-555-1234">
     <mat-icon matSuffix>mode_edit</mat-icon>
   </mat-form-field>