stagefright: Fix "add an extra buffer to ANW's BUfferQueue"

OMAP devices, such as maguro, don't work properly with an extra buffer.
This fixes the commit 2bce3e06f60a8d60c81261b0438d0cc6f2bbe7d1.

Change-Id: Id78442831e95b6021ea8b6d3648678db094f4565