[media] rcar-vin: use rvin_reset_format() in S_DV_TIMINGS

Use rvin_reset_format() in rvin_s_dv_timings() instead of just resetting
a few fields. This fixes an issue where the field format was not
properly set after S_DV_TIMINGS.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>