media: dvb: Verify filter is still active after stalling

While stalling on filter's output buffer in PULL mode,
the filter might be stopped by the user. Need to verify
filter's status once stalling is finished and stop further
processing of the filter's data.

CRs-Fixed: 552100
Change-Id: I66c267dd8b4e71cb948bc14138c766c81ec2a943
Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>