[media] v4l: vsp1: sru: Fix the intensity control default value

The default value isn't set and defaults to 0, which isn't in the 1-6
min-max range. Fix it by setting the default value to 1.

This shoud have been caught when checking the control handler error
field at initialization time, but the check was missing. Add it.

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