media: dvb: Fix PID removal from a filter

When removing a PID from a filter, the dmxdev_feed representing this PID
should be removed from the list of the filter's feeds, and its memory
should be freed.

Change-Id: I8e9f2d69e9c6a907eb6be2d07429e3448ad4e547
Signed-off-by: Liron Kuch <lkuch@codeaurora.org>