media: cadence: csi2rx: Turn subdev power on before starting stream

The subdevice power needs to be turned on before the stream is started.
Otherwise it might not be in the proper state to stream the data.

For some reason, it is observer with OV5640 that turning the power off
when stopping the stream causes the next stream to freeze infinitely. So
leave it on for now until this issue is root caused.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>