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.

http://review.cyanogenmod.org/#/c/57702/

Change-Id: I0ff0ab064c1ac16a128bb3f24d4a473b3164f36d
libnbaio: Fix previous get_presentation_position commit

The previous commit has no effect because HAVE_PRE_KITKAT_AUDIO_BLOB is
actually never defined.

http://review.cyanogenmod.org/#/c/58157/

Change-Id: Ic41b5f02c2cee741aaacce6da1839001a49b9410