sys/v4l2/: Init some structs to zero before we pass them to ioctl, which avoids valgrind warnings.  Also fix a small ...

Original commit message from CVS:
* sys/v4l2/v4l2_calls.c: (gst_v4l2_fill_lists):
* sys/v4l2/v4l2src_calls.c: (gst_v4l2src_fill_format_list):
Init some structs to zero before we pass them to ioctl, which
avoids valgrind warnings.  Also fix a small memory leak.