MPEG4Extractor: Fix opus CSD size

MPEG4Extractor was signally wrong CSD size for csd-0 in case of opus
Instead of signally actual CSD size, size of the array used to hold
the header was being sent.

Bug: 132692852
Test: Manually verified using AMediaExtractor based test application
Change-Id: I88f247a24ab09d0a39b32934659705d7bc9d3f7d