avdevice/dv1394: Use av_freep() to avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avdevice/dshow: Use av_freep() to avoid leaving stale pointers in memory

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avdevice/dshow: Remove unneeded NULL checks

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>