media: dvb: fix the ION output buffer memory leak

Current code does not release the reference to ION buffers
when closing the decoder instance and this causes memory leak
problem. The changes are made to fix the problem by releasing
ION buffers when the decoder instance is closed.

Change-Id: Ice4d20243c99c6db538da67e275beb85b5fab5c5
Signed-off-by: Haifeng Xu <haifeng@codeaurora.org>