stagefright: don't update meta for the same buffer

Even in dynamic ANW buffer mode, if the graphic buffer
is not changing, send sPreset instead of the same graphic
buffer, so that OMX server side doesn't update the meta.

In theory it should make no difference, however when the
same buffer is parcelled again, a new handle could be
created on server side, and some decoder doesn't recognize
the handle even if it's the same buffer.

bug: 33186735
Change-Id: Iff9e2958b90778ac37f93e74cb9cec1b89a9b5b8