media: vivid: free bitmap_cap when updating std/timings/etc.

When vivid_update_format_cap() is called it should free any overlay
bitmap since the compose size will change.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by:  <syzbot+0cc8e3cc63ca373722c6@syzkaller.appspotmail.com>
Cc: <stable@vger.kernel.org>      # for v3.18 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>