LibAAH_RTP: Release TX Group on error.

Immedately release any TX group a player is holding upon entering the
error state.  Once in the error state, the only way out for a media
player it to be completely reset (destroying the player at the
tx_player level of things).  There is really no point in holding on to
a tx group once the player is in the error state.

Change-Id: If5442a32e012b5596789078b0790ed73fa842629