media: i2c: imx290: Simplify imx290_set_data_lanes()

There's no need to check for an incorrect number of data lanes in
imx290_set_data_lanes() as the value is validated at probe() time. Drop
the check.

The PHY_LANE_NUM and CSI_LANE_MODE registers are programmed with a value
equal to the number of lanes minus one. Compute it instead of handling
it in the switch/case.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>