[media] v4l: vsp1: sru: Make the intensity controllable during streaming

The control value is currently stored in the SRU structure by the
control set handler and written to the hardware at stream on time,
making control set during streaming ineffective. Fix it by writing to
the registers from within the control set handler.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>