media: synopsys: hdmirx: Count dropped frames

The sequence number communicate the lost frames to userspace. For this
reason, it must be incremented even when a frame is skipped. This allows
userspace such as GStreamer to report the loss.

Fixes: 7b59b132 ("media: platform: synopsys: Add support for HDMI input driver")
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>