libnbaio: Don't call get_presentation_position for pre KitKat blobs

This fixes a crash with the HTC Tegra3 audio blob where
mStream->get_presentation_position is not NULL but pointing to a unknown
position in memory.

Change-Id: I74855a4c3123a520379a54310d8674e381357e8b
pre-kitkat audio policy blobs re-activated.

Change-Id: Idfcb03d0a4aa0a099bf5a17b7bf592ab402e3255