media: rzv2h-ivc: Fix FM_STOP register write

media: rzv2h-ivc: Fix FM_STOP register write

Bit 20 should be written in this register to stop frame processing.
So fix that, as well as the poll condition.

Cc: stable@vger.kernel.org
Fixes: f0b3984d821b ("media: platform: Add Renesas Input Video Control block driver")
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Barnabás Pőcze <barnabas.pocze+renesas@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>