stagefright aacenc: Don't address a Word32 with a Word16 pointer

Currently, a pointer to a Word32 is used as a pointer to Word16, which
doesn't work as intended on big endian architectures.

This change needs to be analyzed and tested properly so that it doesn't
cause issues with overflows in these variables. Another solution would be
to change all the scf arrays to 32 bit instead.

Change-Id: I53d9eb83bdaf8d3b1530eb5064dd10b08bce737a