media: dvb: Fix un-mapping of external buffers

The output buffers of demux filters can be set in decoder
and in non-PES filters, it is separate from the video output
buffers. When filter is stopped the buffer should be un-mapped
always if it was mapped previously regardless of the filter's type.

Change-Id: I5e0562b23e983a9c624be2dd71612ef23f3b50d0
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>
Signed-off-by: Neha Pandey <nehap@codeaurora.org>