MacOS Zero Copy Capture: Fix CMSampleBufferScopedAccessPermission

This should release the CMSampleBuffer in the destructor, not the
constructor.

Bug: 1125879
Change-Id: Idb266a891fdadaf16a0469e821644c2a1b78e63f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2482245Reviewed-by: Markus Handell <handellm@google.com>
Commit-Queue: Markus Handell <handellm@google.com>
Cr-Commit-Position: refs/heads/master@{#818320}

media/capture/video/mac/video_capture_device_avfoundation_mac.mm

@@ -58,10 +58,8 @@ class CMSampleBufferScopedAccessPermission
     : public media::VideoCaptureDevice::Client::Buffer::ScopedAccessPermission {
  public:
   CMSampleBufferScopedAccessPermission(CMSampleBufferRef buffer)
-      : buffer_(buffer, base::scoped_policy::RETAIN) {
-    buffer_.reset();
-  }
-  ~CMSampleBufferScopedAccessPermission() override {}
+      : buffer_(buffer, base::scoped_policy::RETAIN) {}
+  ~CMSampleBufferScopedAccessPermission() override { buffer_.reset(); }
 
  private:
   base::ScopedCFTypeRef<CMSampleBufferRef> buffer_;