media: staging: max96712: Constify static v4l2_subdev_ops

media: staging: max96712: Constify static v4l2_subdev_ops

The only usage of max96712_subdev_ops is to pass its address to
v4l2_i2c_subdev_init() which takes a pointer to const struct
v4l2_subdev_ops as argument. Make it const to allow the compiler to put
it in read-only memory.

Link: https://lore.kernel.org/linux-media/20211127094945.27985-1-rikard.falkeborn@gmail.com
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Reviewed-by: Niklas S\xF6derlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>