media: i2c: rdacm2x: properly set subdev entity function

The subdevice entity function was left unset, which produces a warning
when probing the device:

mxc-md bus@58000000:camera: Entity type for entity rdacm20 19-0051 was
not initialized!

This patch will set entity function to MEDIA_ENT_F_CAM_SENSOR and leave
flags unset.

Fixes: 34009bff ("media: i2c: Add RDACM20 driver")
Fixes: a59f853b ("media: i2c: Add driver for RDACM21 camera module")
Signed-off-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>
Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>