drivers: media: demux: fixing demux metadata freeing issue

DTV channel switch failed because DMX allocate continuous
memory was failing. It was caused by memory leak in DMX.
Hence populate correct descriptor to free the demux metadata.

Change-Id: I043e9c94e00f04015ad8a2ce4b72ef9b291b9bab
Signed-off-by: rjeyaraj <rjeyaraj@codeaurora.org>