Update documentation for the WakeLock module to reflect the new mojo types

The README.md file was out-of-sync after recent migrations, let's fix it.

Bug: 955171, 978694
Change-Id: I3d02f446a161309d54516d9f35bd4720fb40ec64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1837911Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#702755}

third_party/blink/renderer/modules/wake_lock/README.md

@@ -101,9 +101,9 @@ This is an implementation detail, but the code handling wake locks in `VideoWake
 
 ```c++
 mojo::Remote<mojom::blink::WakeLockService> wake_lock_service;
-device::mojom::blink::WakeLockPtr wake_lock;
+mojo::Remote<device::mojom::blink::WakeLock> wake_lock;
 execution_context->GetInterface(wake_lock_service.BindNewPipeAndPassReceiver());
-wake_lock_service->GetWakeLock(..., mojo::MakeRequest(&wake_lock));
+wake_lock_service->GetWakeLock(..., wake_lock.BindNewPipeAndPassReceiver());
 wake_lock_->RequestWakeLock();
 ```